According to the official website of the Sudak administration, the black spots have spread out along the bank from the Alchak cape to Sudak fortress, having substantially contaminated the city beach. The townspeople also found the dead birds in fuel oil on the waterfront.
Presumably, the oil was released from cargo ship that came in Sudak bay during a storm.
The cleaning works on the beach is due to start after taking samples by the environmental service.
Reference. A heavy petroleum fraction, as that of oil, is the most harmful to the environment, flora and fauna.