These data sets spans multiple oceanographic, chemical, physical, and geomorphological layers. Bathymetric complexity was captured through broad- and fine-scale Bathymetric Position Indices, along with seafloor depth, slope, and ruggedness. Seafloor characteristics included sediment type* and wave exposure estimates. Water column properties were described using measurements of oxygen, salinity, temperature, pH, and nutrient concentrations (nitrate and phosphate) at both bottom and surface layers, each described by mean values and standard deviations. Stratification were characterized by Secchi depth, mixed layer depth, and sea ice concentration. Productivity was approximated by chlorophyll-a concentration. Surface and subsurface variability in wave conditions and satellite-derived sea surface temperature were also collected. Swedish sediment information published with permission from the Swedish Maritime Authority: Decision 23-06009 (12 Sep 2024). To prepare the layers, we applied a procedure designed to iteratively extrapolate missing values in a raster layer by applying a moving window mean filter. It first aligns the input raster to the target grid (Baltic Sea grid at 250 m resolution) using a specified projection method, then repeatedly fills in missing data based on the mean of neighboring cells within a circular window of user-defined size (2 in this case). This iterative process continues until either all missing values are filled or a predefined number of iterations is reached, with early termination if convergence occurs. This procedure ensures that extrapolation respects the spatial extent of the reference grid and provides progress updates during processing. This metadata covers following predictor layers: Bottom Oxygen (Mean) - Mole concentration of dissolved molecular oxygen in sea water at the bottom (µmol/L) Bottom Oxygen (CV) - Coefficient of variation of dissolved molecular oxygen in sea water at the bottom (%) Bottom Salinity (Mean) - Sea water salinity at seafloor (PSU) Bottom Salinity (CV) - Coefficient of variation of sea water salinity at seafloor (%) Bottom Temperature (Mean) - Sea water potential temperature at seafloor (ºC) Bottom Temperature (CV) - Coefficient of variation of sea water potential temperature at seafloor (%) Broad-Scale Bathymetric Position Index - Bathymetric position index, ratio of average depth within 4 km radius to average depth within 20 km radius (m) Chlorophyll-a (Mean) - Mass concentration of chlorophyll a in sea water (mg/m³) Chlorophyll-a (CV) - Coefficient of variation of mass concentration of chlorophyll a in sea water (%) Coarse substrate - Coarse substrate probability of occurrence (%) Depth attenuated exposure at the seafloor - Depth attenuated exposure at the seafloor Distance from the coastline - Distance from the coastline (m) Distance from the nearest river - Distance from the nearest river (m) Fine-Scale Bathymetric Position Index - Bathymetric position index, ratio of average depth within 500 m radius to average depth within 5 km radius (m) Hard substrate - Hard substrate probability of occurrence (%) Mixed Layer Depth (Mean) - Ocean mixed layer thickness defined by sigma theta (m) Mixed Layer Depth (CV) - Coefficient of variation of ocean mixed layer thickness defined by sigma theta (%) Sand substrate - Sand substrate probability of occurrence (%) Sea Ice Concentration (Mean) - Sea ice fraction (%) Sea Ice Concentration (CV) - Coefficient of variation of sea ice fraction (%) Sea surface height (Mean) - Sea surface height above sea level Sea surface height (CV) - Coefficient of variation of sea surface height above sea level (%) Seafloor Depth - Depth in meters below sea surface (m) Seafloor Rugosity within 3 cell radius - Rugosity within 3 cell radius Seafloor Slope - Steepness of the seafloor slope in degrees (Degrees) Secchi Depth (Mean) - Secchi depth of sea water (m) Secchi Depth (CV) - Coefficient of variation of secchi depth of sea water (%) Soft substrate - Soft substrate probability of occurrence (%) Surface Ammonium (Mean) - Mole concentration of ammonium in sea water (µmol/L) Surface Ammonium (CV) - Coefficient of variation of mole concentration of ammonium in sea water (%) Surface Carbon Dioxide (Mean) - Surface partial pressure of carbon dioxide in sea water (µatm) Surface Carbon Dioxide (CV) - Coefficient of variation of surface partial pressure of carbon dioxide in sea water (%) Surface Nitrate (Mean) - Mole concentration of nitrate in sea water (µmol/L) Surface Nitrate (CV) - Coefficient of variation of mole concentration of nitrate in sea water (%) Surface Oxygen (Mean) - Mole concentration of dissolved molecular oxygen in sea water at the surface (µmol/L) Surface Oxygen (CV) - Coefficient of variation of mole concentration of dissolved molecular oxygen in sea water at the surface (%) Surface pH (Mean) - Sea water pH reported on total scale (pH) Surface pH (CV) - Coefficient of variation of sea water pH reported on total scale (%) Surface Phosphate (Mean) - Mole concentration of phosphate in sea water(µmol/L) Surface Phosphate (CV) - Coefficient of variation of mole concentration of phosphate in sea water (%) Surface Primary Productivity (Mean) - Net primary production of biomass expressed as carbon per unit volume in sea water (mg C/m³/day) Surface Primary Productivity (CV) - Coefficient of variation of net primary production of biomass expressed as carbon per unit volume in sea water (%) Surface Salinity (Mean) - Sea water salinity at surface (PSU) Surface Salinity (CV) - Coefficient of variation of sea water salinity at surface (%) Surface Temperature (Mean) - Sea water potential temperature at surface (ºC) Surface Temperature (CV) - Coefficient of variation of sea water potential temperature at surface (%) Terrain Aspect - Aspect, i.e., direction in which the slope is facing out of 360 degrees (N, S, E, W) Wave Height Max (Mean) - Sea surface wave significant height (m) Wave Height Max (CV) - Coefficient of variation of sea surface wave significant height (%) * Swedish sediment information published with permission from the Swedish Maritime Authority: Decision 23-06009 (12 Sep 2024).

Dataset description: This spatial dataset displays catchment areas of the Baltic Sea sub-basins for which the nutrient input to the marine environment and the fulfilment of the maximum allowable inputs of nutrients (MAI) are assessed. Attributes to the polygonal features reflect results of the latest assessment of total normalized input of total nitrogen (TN) and total phosphorus (TP) to the sub-basin from all pathways (riverine, direct, airborne), which are used as HELCOM Core indicator to assess progress towards maximum allowable input (MAI) of nutrients to the Baltic Sea Inputs of nutrients - HELCOM indicators. The assessment takes into account statistical uncertainty which is added to the computed input value. Thus, the fulfilment of MAI means that the nutrient input after adding the statistical uncertainty is below the agreed maximum allowable input value. Attributes TN status and TP status indicate whether MAI is fulfilled or not which is visualized in a simple traffic light colour scheme. The green colour of a catchment indicates that input plus statistical uncertainty was lower than MAI, red colour - input (without statistical uncertainty) was higher, and yellow indicates that input value was lower than MAI but statistical uncertainty does not allow to determine whether MAI was fulfilled. The assessment is performed in accordance with the HELCOM Guidelines for the annual and periodical compilation and reporting of waterborne pollution inputs to the Baltic Sea (HELCOM PLC-Water Guideline). Dataset content: Polygonal feature class contains the following attributes: Sub-basin code (subb_code): Code of the Baltic Sea sub-basin (used for PLC assessment) MAI of total nitrogen (MAI_TN): Maximum allowable input of total nitrogen to respective sub-basin (tons/year) MAI of total phosphorus (MAI_TP): Maximum allowable input of total phosphorus to respective sub-basin (tons/year) Total nitrogen (TN): assessed input of total nitrogen to respective sub-basin (tonnes/year) Total phosphorus (TP): assessed input of total phosphorus to respective subbasin (tonnes /year Total nitrogen uncertainty (TN_uncert): statistical uncertainty of the assessment (tonnes /year) Total phosphorus uncertainty (TP_uncert): statistical uncertainty of the assessment (tonnes /year) Total nitrogen status (TN_status): fulfilment of MAI for TN (fulfilled, not fulfilled, undefined). Total phosphorus status (TP_status): fulfilment of MAI for TP (fulfilled, not fulfilled, undefined). Catchment area (Area): in square kilometres. Year (Year). The following Baltic Sea sub-basin codes are used in the dataset: BAP-BALTIC PROPER; BOB-BOTHNIAN BAY; BOS-BOTHNIAN SEA; GUF-GULF OF FINLAND; GUR-GULF OF RIGA; KAT-KATTEGAT; DS-Danish Straights. Visualization: Map of fulfilment of MAI for nitrogen input to the Baltic Sea - visualizes catchment areas of the Baltic Sea sub-basins in relation to fulfilment of maximum allowable inputs of total nitrogen. Map of fulfilment of MAI for phosphorus input to the Baltic Sea - visualizes catchment areas of the Baltic Sea sub-basins in relation to fulfilment of maximum allowable inputs of total phosphorus. Data update: Metadata is updated by HELCOM Secretariat annually after adoption of indicator report. The dataset is updated by HELCOM Secretariat annually after adoption of indicator report.

Dataset description: The dataset contains annually reported data on water flow, input of nutrients and selected hazardous substances to the Baltic Sea from monitored rivers and unmonitored areas within its catchment area. The data, obtained through national monitoring programmes, is reported by all Contracting Parties to the HELCOM (PLC-water) database as part of HELCOM Pollution Load Compilation (PLC) process. The input from transboundary rivers reflects the whole river catchment including its transboundary parts.. All data is quality assured and approved by Contracting Parties to HELCOM in accordance with the HELCOM Guidelines for the annual and periodical compilation and reporting of waterborne pollution inputs to the Baltic Sea (HELCOM PLC-Water Guideline). Dataset content: The dataset contains the following information: Source name. Name of monitored river or unmonitored area. Source code. The source code refers to the code used in the PLC-water database for the monitored or unmonitored sub-catchments. Country code. The country code indicates the country within the Baltic Sea drainage area (DK; EE; FI; DE; LV; LT; PL; RU; SE;). Sub-basin code. The sub-basin code refers to the Baltic Sea sub-basin used in HELCOM assessment of inputs of nutrients and hazardous substances (ARC; BAP; BOB; BOS; GUF; GUR; KAT; SOU; WEB). Parameter. Parameters reported by the contracting parties to the Helsinki Convention to assess riverine inputs of nutrients and selected hazardous substances. : AOX; BOD5; BOD7; Cd*; COD-Cr; COD-Mn; Cr; Cu; FLOW; Hg*; Ni; NNH4*; NNO2*; NNO3*; NNO3; NTOT*; Oil; Pb*; PPO4;* PTOT*; SPM; TOC; Zn. (tonnes/year or flow in m3/s). Year. Year of observation. *Mandatory parameters for annually reported riverine data. Other parameters are voluntary. Country codes used in the dataset correspond to: DK-DENMARK; EE-ESTONIA; FI-FINLAND; DE-GERMANY; LV-LATVIA; LT-LITHUANIA; PL-POLAND; RU-RUSSIA; SE-SWEDEN; The Baltic Sea sub-basin codes used in the dataset are: ARC-ARCHIPELAGO SEA; BAP-BALTIC PROPER; BOB-BOTHNIAN BAY; BOS-BOTHNIAN SEA; GUF-GULF OF FINLAND; GUR-GULF OF RIGA; KAT-KATTEGAT; SOU-SOUND; WEB-WESTERN BALTIC. Visualization: The dataset can be retrieved from the HELCOM PLC-Water database and visualized utilizing an online user interface. The following filters are available to generate the dataset: Source of input: monitored river, unmonitored area. Multiple selection possible Country: DENMARK; ESTONIA; FINLAND; GERMANY; LATVIA; LITHUANIA; POLAND; RUSSIA; SWEDEN. Multiple selection possible. Baltic Sea sub-basin: ARCHIPELAGO SEA; BALTIC PROPER; BOTHNIAN BAY; BOTHNIAN SEA; GULF OF FINLAND; GULF OF RIGA; KATTEGAT; SOUND; WESTERN BALTIC. Multiple selection possible. Year: the first and the last year of the data request (1995-20…) Parameter: AOX; BOD5; BOD7; Cd; COD-Cr; COD-Mn; Cr; Cu; FLOW; Hg; Ni; NNH4; NNO2; NNO23; NNO3; NTOT; Oil; Pb; PPO4; PTOT; SPM; TOC; Zn. Only one parameter can be selected. Data update: Metadata is updated by the HELCOM Secretariat annually by 1 April. The dataset is updated annually and becomes publicly available in accordance with PLC-Water Guidelines, which details the procedures for reporting data to the HELCOM pollution load compilation (PLC) and the release of PLC products based on reported data.

This dataset contains disposal sites reported by HELCOM Contracting Parties, according to the HELCOM Recommendation 36/2 (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). The disposal sites are grouped by spatial data type to pointwise, line and polygon datasets. Data covers the years 2006-2023. The data format is defined in the HELCOM Guidelines for management of dredged material at sea (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). Attribute information (heading for downloadable shapefile): Helcom site ID (Helcom_sit): Unique id for deposit site Dredging ID (Dredging_I): Dredging site id, where material originates from Unique ID (Unique_ID): Unique id for each depositing activity (Helcom site ID + Dredging ID + year) Site name (Site_name): Name of the deposit site Type of area dredged (Type_of_ar): Type of area that was dredged (e.g. harbour or sea) Dredging activity (Dredging_a): Maintenance or capital dredging Material deposited (Material_d): The type of material deposited (e.g. sand, silt) Amount deposited (tonnes) (Amount_dep): Amount of material that has been deposited to deposit site, tonnes dry weight Amount beneficial use (tonnes) (Amount_ben): Amount material used for beneficial purposes, tonnes dry weight Beneficial use (Beneficial): Description of beneficial use Year (Year): Year of activity Country (Country): Contracting Party of HELCOM Sub-basin (Sub_basin): HELCOM sub-basin (assessment unit level 2) where activity has taken place Comments (Comments): General comments related to activity Contaminants Cd - SPAH9: Amount of contaminant deposited, in tonnes dry weight Contaminants SPCB7 - MBT : Amount of contaminant deposited, in kilograms dry weight Other contaminants (kg) (Other_cont): Any other contaminant deposited (substance indicated in "notes") Petroleum HC (tonnes) (Petroleum_): Amount of Petroleum HC deposited, in tonnes dry weight HCB - DEHP DBP BBP: Amount of contaminant deposited, in kilograms dry weight Contaminant notes (Contaminan): Notes related to contaminant load Permit (Permit): Deposit site permit reference Quality flag (Quality_fl): Quality flag of data - Quality assured: Data is quality assured either in the annual verification or in a separate quality assurance process by EN DREDS - No quality assurance: Data is not quality assured due to the reason that process has not been carried out - No Quality assurance possible: Data quality assurance process has been made, but it was not possible to find the reference data to verify the parameters

This dataset contains dredging sites reported by HELCOM Contracting Parties, according to the HELCOM Recommendation 36/2 (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). Reporting of dredging sites connected to disposal events became mandatory starting from 2023 data, when the HELCOM Guidelines for Management of Dredged Material at Sea was updated. Before this, reporting of dredging sites was not mandatory, but several Contracting Parties report information about dredging activities. The dredging sites are grouped by spatial data type to point, line and polygon datasets. The dredging site includes a link to corresponding site where the material has been deposited. Attribute information (heading for downloadable shapefile): Dredging ID (Dredging_I): Dredging site id, where material originates from Deposit site (Helcom site ID) (Helcom_sit): Unique id for deposit site Deposit site link (Deposit_si): Link to deposit site, where material from this dredging site is deposited Site name (Site_name): Name of the dredging site Type of area dredged (Type_of_ar): Type of area that was dredged (e.g. harbour or sea) Dredging activity (Dredging_a): Maintenance or capital dredging Material dredged (Material_d): The type of material dredged (e.g. sand, silt) Year (Year): Year of activity Country (Country): Contracting Party of HELCOM Sub-basin (Sub_basin): HELCOM sub-basin (assessment unit level 2) where activity has taken place Quality flag (Quality_fl): Quality flag of data - Quality assured: Data is quality assured either in the annual verification or in a separate quality assurance process by EN DREDS - No quality assurance: Data is not quality assured due to the reason that process has not been carried out - No Quality assurance possible: Data quality assurance process has been made, but it was not possible to find the reference data to verify the parameters

This dataset consists of information and status of the main pollution sources within the Baltic Sea catchment area (the Pollution Hot Spots). The HELCOM pollution Hot Spots were idenitified in 1992 by the HELCOM Joint Comprehensive Action Programme (more information is available on www.helcom.fi). The current status of active and cleaned hot spots is available https://helcom.fi/action-areas/industrial-municipal-releases/helcom-hot-spots/.

This dataset contains disposal sites reported by HELCOM Contracting Parties, according to the HELCOM Recommendation 36/2 (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). The disposal sites are grouped by spatial data type to pointwise, line and polygon datasets. Data covers the years 2006-2023. The data format is defined in the HELCOM Guidelines for management of dredged material at sea (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). Attribute information (heading for downloadable shapefile): Helcom site ID (Helcom_sit): Unique id for deposit site Dredging ID (Dredging_I): Dredging site id, where material originates from Unique ID (Unique_ID): Unique id for each depositing activity (Helcom site ID + Dredging ID + year) Site name (Site_name): Name of the deposit site Type of area dredged (Type_of_ar): Type of area that was dredged (e.g. harbour or sea) Dredging activity (Dredging_a): Maintenance or capital dredging Material deposited (Material_d): The type of material deposited (e.g. sand, silt) Amount deposited (tonnes) (Amount_dep): Amount of material that has been deposited to deposit site, tonnes dry weight Amount beneficial use (tonnes) (Amount_ben): Amount material used for beneficial purposes, tonnes dry weight Beneficial use (Beneficial): Description of beneficial use Year (Year): Year of activity Country (Country): Contracting Party of HELCOM Sub-basin (Sub_basin): HELCOM sub-basin (assessment unit level 2) where activity has taken place Comments (Comments): General comments related to activity Contaminants Cd - SPAH9: Amount of contaminant deposited, in tonnes dry weight Contaminants SPCB7 - MBT : Amount of contaminant deposited, in kilograms dry weight Other contaminants (kg) (Other_cont): Any other contaminant deposited (substance indicated in "notes") Petroleum HC (tonnes) (Petroleum_): Amount of Petroleum HC deposited, in tonnes dry weight HCB - DEHP DBP BBP: Amount of contaminant deposited, in kilograms dry weight Contaminant notes (Contaminan): Notes related to contaminant load Permit (Permit): Deposit site permit reference Quality flag (Quality_fl): Quality flag of data - Quality assured: Data is quality assured either in the annual verification or in a separate quality assurance process by EN DREDS - No quality assurance: Data is not quality assured due to the reason that process has not been carried out - No Quality assurance possible: Data quality assurance process has been made, but it was not possible to find the reference data to verify the parameters

Dataset description: The dataset reflects spatial delineation of monitored and unmonitored catchments used for the assessment of waterborne nutrients inputs to the Baltic Sea sub-basins (Baltic Sea Environmental Fact Sheet) in the HELCOM Pollution Load Compilation. Polygonal features in the dataset cover entire river catchments without distinguishing between sub-catchments located in upstream countries. Some countries even combine unmonitored and monitored parts of river catchments into a single catchment. The Source Code attribute in the dataset corresponds to the Source_Code in the Assessment data on waterborne input of nutrients dataset. The data is reported to the HELCOM Map and Data Service (MADS) and quality assured by Contracting Parties to HELCOM in accordance with the HELCOM Guidelines for the annual and periodical compilation and reporting of waterborne pollution inputs to the Baltic Sea (HELCOM PLC-Water Guideline). Dataset content: Polygonal feature class contains the following attributes: Sub-catchment code (subc_code): Unique code for river catchments and unmonitored areas Sub-catchment name (subc_name): Name of river catchment or unmonitored area River code (r_code): Unique code of the river included in HELCOM PLC assessment. Sub-basin code (subb_code): The Baltic Sea sub-basin where the river drains to. Country code (c_code): The Country on which territory the river mouth is located, for border rivers both are mentioned. Monitoring (monitoring): The monitoring status of the river (M=monitored and U=unmonitored). Marked as monitored only if the catchment has been monitored for the entire time series. Transboundary (transboundary): Listing all countries that have the rivers drainage area on its territory. Area km2 (area_km2): The total area of the catchment in square kilometres. Year (year). Country codes used in the dataset correspond to: DK-DENMARK; EE-ESTONIA; FI-FINLAND; DE-GERMANY; LV-LATVIA; LT-LITHUANIA; PL-POLAND; RU-RUSSIA; SE-SWEDEN. The Baltic Sea sub-basin codes used in the dataset are: ARC-ARCHIPELAGO SEA; BAP-BALTIC PROPER; BOB-BOTHNIAN BAY; BOS-BOTHNIAN SEA; GUF-GULF OF FINLAND; GUR-GULF OF RIGA; KAT-KATTEGAT; SOU-SOUND; WEB-WESTERN BALTIC. Visualization: Map of catchments in the HELCOM Pollution Load Compilation. Data update: Metadata is updated by HELCOM Secretariat annually by 1 April. The dataset is updated by HELCOM Secretariat annually by 1 April.

Dataset description: The dataset contains data on locations of river monitoring stations of nutrients and hazardous substances inputs to the Baltic Sea reported to the HELCOM Pollution Load Compilation (PLC-water) database. The stations are categorized as hydrological (only flow monitoring) and chemical (monitoring of chemical components). The data is reported to the HELCOM database and quality assured by Contracting Parties to HELCOM in accordance with the HELCOM Guidelines for the annual and periodical compilation and reporting of waterborne pollution inputs to the Baltic Sea (PLC-Water Guidelines). Dataset content: Station code (st_code): unique HELCOM PLC code Station name (st_name). River code (r_code): unique HELCOM PLC code. Sub catchment code (subc_code): unique HELCOM PLC code Country code (c_code): DK; EE; FI; DE; LV; LT; PL; RU; SE. Sub-basin code (subb_code): ARC; BAP; BOB; BOS; GUF; GUR; KAT; SOU; WEB. Station category (st_cat): hydrological (H) and chemical (C). Latitude (st_lat). Longitude (st_lon). Reporting year (year). Country codes used in the dataset correspond to: DK-DENMARK; EE-ESTONIA; FI-FINLAND; DE-GERMANY; LV-LATVIA; LT-LITHUANIA; PL-POLAND; RU-RUSSIA; SE-SWEDEN. The Baltic Sea sub-basin codes used in the dataset are: ARC-ARCHIPELAGO SEA; BAP-BALTIC PROPER; BOB-BOTHNIAN BAY; BOS-BOTHNIAN SEA; GUF-GULF OF FINLAND; GUR-GULF OF RIGA; KAT-KATTEGAT; SOU-SOUND; WEB-WESTERN BALTIC. Visualization: Map - point feature class. Legend visualizes two categories of monitoring station: hydrological, chemical. Data update: Metadata is updated by HELCOM Secretariat annually by 1 April. The dataset is updated by HELCOM Secretariat annually by 1 April.

This dataset contains dredging sites reported by HELCOM Contracting Parties, according to the HELCOM Recommendation 36/2 (https://helcom.fi/action-areas/industrial-municipal-releases/dredging/). Reporting of dredging sites connected to disposal events became mandatory starting from 2023 data, when the HELCOM Guidelines for Management of Dredged Material at Sea was updated. Before this, reporting of dredging sites was not mandatory, but several Contracting Parties report information about dredging activities. The dredging sites are grouped by spatial data type to point, line and polygon datasets. The dredging site includes a link to corresponding site where the material has been deposited. Attribute information (heading for downloadable shapefile): Dredging ID (Dredging_I): Dredging site id, where material originates from Deposit site (Helcom site ID) (Helcom_sit): Unique id for deposit site Deposit site link (Deposit_si): Link to deposit site, where material from this dredging site is deposited Site name (Site_name): Name of the dredging site Type of area dredged (Type_of_ar): Type of area that was dredged (e.g. harbour or sea) Dredging activity (Dredging_a): Maintenance or capital dredging Material dredged (Material_d): The type of material dredged (e.g. sand, silt) Year (Year): Year of activity Country (Country): Contracting Party of HELCOM Sub-basin (Sub_basin): HELCOM sub-basin (assessment unit level 2) where activity has taken place Quality flag (Quality_fl): Quality flag of data - Quality assured: Data is quality assured either in the annual verification or in a separate quality assurance process by EN DREDS - No quality assurance: Data is not quality assured due to the reason that process has not been carried out - No Quality assurance possible: Data quality assurance process has been made, but it was not possible to find the reference data to verify the parameters