The CCM2 database covers the entire European continent, including the Atlantic islands, Iceland and Turkey. It includes a hierarchical set of river segments and catchments based on the Strahler order, a lake layer and structured hydrological feature codes based on the Pfafstetter system. This dataset is a subset of Catchment Characterisation and Modelling (CCM) data version 2.1 provided by EU Joint Research Centre (JRC). The CCM2 database covers the entire European continent, including the Atlantic islands, Iceland and Turkey. It includes a hierarchical set of river segments and catchments based on the Strahler order, a lake layer and structured hydrological feature codes based on the Pfafstetter system. For further details, see http://ccm.jrc.ec.europa.eu/php/index.php?action=view=23 The river data contained in CCM2 Geodatabase table MAINRIVERS was clipped with Baltic Sea catchment area (extracted from table Seaoutleats) and erased by table LAKES with ETGeowizards "Erase" tool by HELCOM secretariat. Copyright Statement: The proprietary rights and copyright of the CCM River and Catchment data remain with the European Commission, Joint Research Centre (JRC). Reproduction for non-commercial purposes is authorised, provided the source is acknowledged. Commercial use is not permitted without prior written consent of the JRC. Reports, articles, papers, scientific and non-scientific works of any form, including tables, maps, or any other kind of output, in printed or electronic form, based in whole or in part on the data supplied, must contain an acknowledgement of the form: CCM River and Catchment Database © European Commission - JRC, 2007 as well as a reference to: Vogt, J.V. et al. (2007): A pan-European River and Catchment Database. European Commission - JRC, Luxembourg, (EUR 22920 EN) 120 pp.

Location of water course modifications (trenching, culverting, canalisation). The data was made available by HELCOM Contracting Parties in response to data request. The data was received from Estonia, Finland and Poland. Data reported by Finland and Poland as water course modification were interpreted as pipelines and were included in HELCOM HOLAS 2 Pipelines dataset. The activity was declared as not relevant in Germany and Lithuania. From Latvia, Russia and Sweden no data was reported.

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. The following human activities were combined into the changes to hydrological conditions layer; - Hydropower dams (a 1km2 grid cell in the river estuary was selected) - Water course modification (1 km) - Wind turbines (operational, 0.3 km, linear decline) - Oil platforms (0.5 km, linear decline) 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.

HOLAS II data set on Nuclear power plants discharge water outlets (name, delta temperature of water discharge, heat load) for 2011-2015. The coverage of the data set is full, except for the Leningrad power plant the data is not available.

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.

The dataset contains the location of water course modifications as reported by the Contracting Parties for the period 2016-2021. The data was made available by HELCOM Contracting Parties in response to a data call. The data was reported by Denmark, Estonia, Finland, and Sweden. The use of HOLAS 2 data was requested by Estonia and Sweden. The activity was declared as not relevant in Germany and Latvia. Attribute specification and units (points and polygons): Year: Year of construction, especially if built between 2016-2021 Type: Structure type as listed on the data call (canalisation, culverting/trenching, causeway, damn/weir, other) Notes: Notes regarding the data Status: The status of the structure, if available Dimension: The dimension of the outlet, if available Original ID: Original identification used by the Contracting Party Attribute specification and units (lines): ID NAMESPACE STATUS KATEGORI TYPE JOURNAL_NR NOTE REGISTERTI REGISTER_1 VIRKNINGFR VIRKNINGTI EJER FAERDIGMEL REGISTRERI VIRKNINGSA

Illegal oil discharges data is based on airborne surveillance supplemented with remote sensing equipment in the Baltic Sea Area carried out by HELCOM Contracting Parties within HELCOM IWGAS group. Aerial surveillance is limited within Russia and Latvia.

Illegal oil discharge data is based on airborne surveillance supplemented with remote sensing equipment in the Baltic Sea Area carried out by HELCOM Contracting Parties within HELCOM IWGAS group. Years 2016-2021 were extracted from the HELCOM Illegal oil discharges database. Attribute specification and units HELCOM_ID Country Year Spill_ID FlightType Date Time_UTC Wind_speed Wind_direc Latitude Longitude Length_km Width_km Area_km2 Spill_cat EstimVol_m Polluter Category Casefile Remarks

Polluting ship accidents is based on reporting of shipping accidents done by HELCOM Contracting Parties to produce annual within HELCOM MARITIME group. Data was available for 2011-2013

HOLAS 3 data set on Nuclear power plants discharge water outlets for 2016-2021. The coverage of the data set is full, except for the Leningrad power plant the data is not available. Attribute specifications and units NPP: name of the plant TWh_2016 - 2021: Heat Load (TWh) per year average: Average temperature change of coolant water (°C)