Energinet.dk has commissioned NIRAS and subcontractors to conduct the environmental impact assessment (EIA) for the construction and operation of the largest offshore wind farm, called Kriegers Flak, in Denmark to date. The preliminary study area of 180 km2 around the projected wind farm is located approximately 15 km east of the east coast of Zealand, in the South-western part of the Baltic bordering the EEZ (Exclusive Economic Zone) of Sweden and Germany. The exact wind farm area will consist of two sections, 44km2 to the west and 88 km2 to the east of the study area. As part of the EIA, DCE/Aarhus University and DHI have conducted the baseline studies on marine mammals to assess the impacts of the construction and operation of a wind farm at Kriegers Flak. Three species of marine mammals are known to occur regularly in the area of Kriegers Flak: harbour porpoises (Phocoena phocoena), harbour seals (Phoca vitulina) and grey seals (Halichoerus gryphus). All three species are protected by international agreements and legislation, including the EU Habitats Directive, the Convention for protection of Migratory Species (Bonn-convention), ASCOBANS, HELCOM as well as national legislation. The purpose of this report is to outline the baseline conditions for the marine mammals occurring in the Kriegers Flak area by providing detailed information on their spatial and temporal use of the area, and to evaluate the potential effects of the construction, operation and dismantling of the planned wind farm on the marine mammals.