"Tests of water samples made by Russian weather service experts on November 13 showed 2.5 milligrams per liter, which is 50 times above the acceptable concentration level," the service said in a statement.
The service said the storm in the Kerch Strait had prevented experts from taking the samples until Tuesday.
In Sunday's disaster, a further four ships sank, and at least six sailors died. The Russian Emergency Situations Ministry said earlier 2,000 metric tons of fuel oil had spilled into the sea, and fuel was continuing to spill out. The sunken dry-cargo vessels have about 7,000 metric tons of sulphur on board.
Some reports said another six vessels ran aground and two more tankers were damaged.
"An examination of the shore of the Tuzla Promontory [in the Kerch Strait] showed that the entire coastline overlooking the Black Sea is contaminated with fuel oil. Oil products have penetrated 20-30 cm deep into the shore and have made a strip about 10 meters wide," the statement said.
Experts also said the oil spill stretches 20-30 meters into the sea. They said storms would continue to wash oil products onto the shore.
Weather forecasters said the weather in the area would be relatively calm without precipitation on Wednesday. But in the next two days, the weather is forecast to get worse, with wind velocity reaching 19 meters a second and waves rising up to 2.5 meters.
Some 4,000 volunteers will help clean up the environmental aftermath in the area, the head of the World Wildlife Fund (WWF) in Russia said on Wednesday. The WWF also called on Russia to adopt stricter laws on sea transports of oil in order to prevent future disasters.
Earlier on Wednesday, a Russian emergencies ministry spokesman said about 870 metric tons of oil-contaminated waste had been collected in the area of Port Kavkaz to date. Russia has been supplying absorbents to clean up the sea.
Some 9,000 fish and 30,000 birds have been killed by the pollution in the strait, earlier reports said.
Rescuers have meanwhile resumed the search for five missing sailors from the sunken dry freighter Nakhichevan.
