Rosneft has strongly denied that any of its regional subsidiaries are the source of an oil spill discovered in Russia's sector of the Black Sea this week.

Russia's largest oil producer was quick to release a statement denying culpability after oil was spotted on a beach near the port of Tuapse on 24 May.

The country’s environmental watchdog, Rosprirodnadzor, estimated the size of the polluted sea area at more than 1.1 square kilometres.

A brief investigation — organised by the watchdog with the help of divers — revealed that oil is seeping from a large-diameter pipe used by the city of Tuapse to dump sewage into the deep-water area of the Black Sea about 800 metres from shore.

Rosneft said that two of its subsidiaries — involved with the Tuapse refinery and the Tuapse oil and products export terminal — have provided supplies and equipment, such as booms, to collect oil from the sea surface.

Source a mystery

Local authorities have suggested that the sewage pipe could have been illegally used by an as yet unknown company to dump an unidentified volume of oil or oil products.

Rosneft said none of its subsidiaries operate within the onshore area that the sewage pipe crosses on its way to the sea.

The Tuapse sea port authority said it is not “privy to the accident”.

A representative of the regional department of Rosprirodnadzor said it has opened an investigation to identify the place where oil entered the sewage system.

The watchdog added that, following measures to contain the spill, the oil is not seen as a danger to the coastline.

Russia has been hit with several oil spills in May, the largest one in the Komi and Nenets region in the north of the country.

Remedial effort in the north

Oil producer Lukoil and regional departments of the Ministry of Emergency Situations are still collecting oil and continuing remedial efforts along the Kovla, Usa and Pechora rivers after the rupture of a pipeline exporting oil from the Oshskoye field, operated by Lukoil-Komi.

The spill was discovered on 11 May after oil travelled more than 100 kilometres from the site of the rupture along the Kolva River.

Local environmental group Save Pechora Committee reported accounts of residents who have spotted oil hundreds of kilometres downstream from the accident site.

The Kolva River, which is a source of water supply and fishing grounds, appears to have been heavily affected, according to the group.