This dataset contains all indicator and assessment results and data for the State of the Baltic Sea (HOLAS II) 2017 version. Final 2018 versions are included separately in HELCOM Map and Data service and metadata catalogue. All datasets for HOLAS II and associated metadata were here compiled. The datasets are: Abundance of coastal fish key functional group cyprinids Abundance of coastal fish key functional group piscivores Abundance of coastal fish species Abundance of salmon spawners and smolt Abundance of waterbirds in the breeding season Abundance of waterbirds in the wintering season Chlorophyll a status Cyanobacterial bloom Dissolved inorganic nitrogen Dissolved inorganic phosphorous Distribution of grey seals Distribution of harbour seals Distribution of ringed seals Eutrophication assessment insitu data Heavy metals – Cadmium (Cd) levels Heavy metals – Lead (Pb) levels Heavy metals – Mercury (Hg) levels Hexabromocyclododecane (HBCDD) levels Integrated biodiversity status assessment for benthic habitats Integrated biodiversity status assessment for fish Integrated biodiversity status assessment for grey seals Integrated biodiversity status assessment for harbour porpoises Integrated biodiversity status assessment for pelagichabitats Integrated biodiversity status assessment for ringed seals Integrated biodiversity status assessment for seals Integrated contamination status assessment Integrated eutrophication status assessment Oxygen det PCB dioxin and furan Perfluorooctane sulphonate (PFOS) Polyaromatic hydrocarbons (PAH) and their metabolites Polybrominated diphenyl ethers Cesium-137 in fish Cesium-137 in flatfish Cesium-137 in herring Cesium-137 in seawater Malformed embryos of amphipods State of the soft bottom macrofauna community TBT and imposex Total nitrogen Total phosphorous Trend in arrival of new non-indigenous species Water clarity Zooplankton mean size and total stock MSTS

The seals' distribution maps show the distribution and abundance of grey, harbour and ringed seals across the Baltic Sea. The ecosystem component maps on mammals' distribution were drafted by EG MAMA harbour porpoise and seal distribution teams. The maps were prepared as expert-derived distribution categories to be used in the HELCOM Third Holistic Assessment of the Ecosystem health of the Baltic Sea.

Physical loss pressure layer combines all human activities that cause physical loss of seabed. The pressure is given as area lost in each cell (km2). For the polygon datasets the area was assumed to be the lost area. For line and point datasets spatial extents were calculated with buffers (below in brackets). If no buffer extent is indicated, the data was reported as polygon. The human activities used for the physical loss pressure: Land claim - Area of polygon or 50 m buffer for points, 30m buffer for lines. Area of polygon - buffered line or point data, equals lost area. Watercourse modification - 50 m buffer. Area of polygon, buffered line or point data, equals lost area. Coastal defence and flood protection - 50 m buffer for lines, area of polygon. Area of polygon, buffered line or point data, equals lost area. Extraction of sand and gravel - Area of polygon. Area of polygon equals lost area. Dredging (capital) - Area of polygon or a 25/50 m buffer for <5000 m3 / >5000m3 sites. Area of polygon, buffered line or point data, equals lost area. Oil platforms - 25 m buffer. Buffered point data, equals lost area. Pipelines - 15 m buffer around cables with operational status. Area of polygon, buffered line or point data, equals lost area. Wind farms - 30 m buffer around each turbine with operational status. Buffered point data, equals lost area. Cables - 1.5 m buffer around cables with operational status. Buffered line data, equals lost area. Harbours - Polygon with 200 m buffer. Area of polygon, buffered line or point data, equals lost area. Marinas and leisure harbour - Point with 200 m buffer. Buffered point data, equals lost area. Bridges - 2 m buffer. Buffered line data, equals lost area. Finfish mariculture - 150 m buffer. Buffered point data, equals lost area. Shellfish mariculture - Area of polygon, 150 m buffer for points. Buffered point data, equals lost area. Activities are combined and potentially overlapping areas are removed. Dataset is clipped with coastline. Combined layer is intersected with 1 km grid to calculate % of area lost within a cell.

This dataset is built from following Human activities datasets: • https://metadata.helcom.fi/geonetwork/srv/eng/catalog.search#/metadata/3d6bd6f9-72d5-40cf-aaaa-b7c0c18878e3 • https://metadata.helcom.fi/geonetwork/srv/eng/catalog.search#/metadata/41da8e41-d907-419d-8841-f95062d002e7 The game hunting of seabirds data (see separate metadata): The total number of hunted seabirds were averaged over 2016-2021 (number of hunted seabirds / year). The area of the reporting unit was used to calculate the number of hunted seabirds / km2 and the data was converted to 1km x 1km grid. The predator control of seabirds data (see separate metadata): The total number of hunted cormorants were averaged over 2016-2021 (number of hunted cormorants / year). The area of the reporting unit was used to calculate the number of hunted cormorants / km2 and the data was converted to 1km x 1km grid. The two datasets were first separately log transformed and then summed, to get the total value for each grid cell. Zero values were given to all grid cells with no reported seabird hunting activity. The layer was normalized.

Hunting of Grey, ringed and harbour seals (2016-2021) Varying reporting units, from counties to HELCOM subdivisions. The number of hunted seals (2016-2021) per unit was normalized with 0,5 set as the quota for hunting, per species and per year. The values were averaged for each species and those values were averaged for the unit to form the final pressure value.

Input of impulsive anthropogenic sound includes impulsive events from 2016-2021 • Seismic surveys (HELCOM-OSPAR Registry; national data call submissions as lines in the folder of data) • Explosions (HELCOM-OSPAR Registry) • Pile driving (HELCOM-OSPAR Registry) • Airguns (HELCOM-OSPAR Registry) For the different event types, numeric intensity value was used to represent the pressure as categorized in HELCOM-OSPAR Impulsive noise registry. All nationally reported seismic surveys were given intensity values “Very low” (0.25) - Very low (0.25) - Low (0.5) - Medium (0.75) - High (1) The impact distance has not been taken into account due to the different nature of separate datasets used for the pressure layer. We acknowledge that e.g. pile driving and airguns may impact up to 20 km from the source event. The spread of the sound wave depends on the sound frequency, water salinity, temperature and density.

Pressure layer combines all human activities that cause physical disturbance or damage to seabed. For several human activity datasets, spatial extents were given (table below). Buffers with decreasing value rates were applied to represent the impact distance of physical disturbance. The following human activities were combined into the physical disturbance layer; - Cables (under construction, 1 km buffer) - Coastal defence and flood protection (under construction, 500 m buffer) - Deposit of dredged material (500 m buffer for points and areas) - Dredging (maintenance) (500 m buffer for points and areas) - Extraction of sand and gravel (500 m buffer) - Finfish mariculture (1 km buffer) - Fishing intensity 2011-2016 average (subsurface swept area ratio) - Furcellaria harvesting - Pipelines (0,3 km buffer) - Recreational boating and sports - Shellfish mariculture - Shipping density - Wind farms (under construction) (1 km buffer) - Wind farms (operational) (0,1 km buffer) The human activity data sets were first processed separately covering the whole Baltic Sea and then summed together. In this integration, some data layers were down-weighted to arrive at a balanced pressure layer, as described below. High pressure intensity and/or slow recovery (weighting factor 1): Coastal defence and flood protection, Deposit of dredged material, Dredging, Extraction of sand and gravel and Fishing intensity Moderate to high (Weighting factor 0,8): Pipelines and Shipping density Moderate (Weighting factor 0,6): Finfish mariculture, Shellfish mariculture and Wind farms (under construction) Low to moderate (Weighting factor 0,4): Cables Low (Weighting factor 0,2): Maerl and Furcellaria harvesting, Recreational boating and sports and Wind farms (operational) Harbours and marinas were left out from the physical disturbance pressure to avoid double counting due to their representation in the shipping density and recreational boating and sports data sets. Detailed information about this pressure layer can be found in the indicator report.

Pressure layer combines all human activities that cause changes to hydrological conditions. The human activities were presented as point data which were given spatial extents (given below). The pressure value was given as the proportion of the grid cell under the pressure. Water course modification: 1 km buffer[10]. Location of water course modifications used for buffer. Overlaps removed and areas of buffer calculated per each grid cell. The final value was the area of the buffer in each individual cell. Wind farms: 300 m buffer around each turbine classified as operational, with linear decline (Type B decline), composed of 3 rings. Location of operational turbines as points were buffered and values given over linear decline. Oil platforms: 500 m buffer around each turbine with linear decline (Type B decline) composed of 5 rings. Location of oil platforms as points were buffered and values given over linear decline. Hydropower dams: A grid cell in the estuary. Locations of hydropower dams were crossed with rivers and the grid cell located in the end of the river was selected as presence (1) – those that are operational and produces energy. Other values in the grid were considered absence. [10] Extent based on wind farms and cables but expanded to 1 km because hydrological parameters are widely spreading. The human activity datasets were first processed separately covering the whole Baltic Sea and then summed together and overlapping areas were dissolved to remove double counting. Attenuation gradients are assigned to each layer as described above. Area effected decreases when distance from avtivity increases. Layer was normalized.

Input of heat pressure dataset contains delta heat values from warm water discharge of - Discharge of warm water from nuclear power plants - Fossil fuel energy production. Discharge of warm water from nuclear power plants (2016-2021): 1 km buffer with steep decrease around outlet (Type D decline), composed of 4 rings [1]. Average input of heat load (Twh) of discharge of warm water from the nuclear power plant outlets. No data on heat load was available for the Leningrad nuclear power plant; therefore, the average heat load of discharge of warm water from nuclear power plants was given. Fossil fuel energy production (only location available): 1 km buffer with steep decrease around outlet (Type D decline), composed of 6 rings[12]. Heat load 1 (TWh) was given to all production sites, based on the average heat load of an individual production site in Helsinki. Heat load from both layers were summed and the layer was normalized. [1] Extent based on Ilus et al. 1986.

Input of hazardous substances pressure layer is interpolated from CHASE Assessment tool concentration component. The contamination ratio values were calculated with CHASE Assessment tool for hazardous substances monitored in water, sediment and biota. Classified mean contamination ratio was used in the interpolation. Classification is based on the http://stateofthebalticsea.helcom.fi/about-helcom-and-the-assessment/downloads-and-data/. The points were interpolated to cover the entire Baltic Sea with Spline with barriers interpolation method. Please see "lineage" section below for further details on attributes, data source, data processing, etc.