The Green Balkans dataset contains effort-based occurrence records collected during a cetacean monitoring programme in the Bulgarian Black Sea waters, since 2016. The project is led by the Green Balkans NGO and aims to ensure regular monitoring of cetaceans in Bulgarian territorial and shelf waters in the Black Sea. Platforms are motor sailing yachts and at one occasion a fishing vessel. On-board trained marine mammal observers collected data on: survey effort including meteorological conditions and cetacean sightings. Data is provided in the recent OBIS-ENV-DATA format and comprises 2643 georeferenced positions associated with 1663 occurrences of 3 marine taxa. On several occasions, data was recorded only to level of Family or Superfamily. For each recorded sighting, perpendicular distance is recorded.