Soldiers and emergency workers are battling to clean up an oil spill that has reportedly killed some 30,000 birds in the Kerch Strait, by the Black Sea.
There are fears many more birds will die in the coming days
Alexander Tkachev, governor of Russia's Krasnodar region, said the incident was an "ecological catastrophe".
Some 2,000 tons of fuel oil leaked into the straits between the Black Sea and the Azov Sea after a fierce storm broke a tanker apart on Sunday.
About 10 ships sank or ran aground in the region and 20 sailors are missing.
So far, 35 crew members from the stricken vessels have been plucked to safety by rescue teams. The bodies of three sailors were found on Monday morning.
At least two other ships were carrying potentially hazardous cargo when they sank, including nearly 6,000 tons of sulphur.
The Russian tanker Volganeft-139, with more than 4,000 tons of fuel aboard, came apart after it was smashed by 108km/h (67 mph) winds and 5m (16ft) waves in the narrow Kerch Strait between Russia and Ukraine.
Stormy weather is hampering the clean-up operation
Officials estimate that nearly half the tanker load has already leaked out in the water.
"Some 30,000 birds have died and it's not possible to count how many fish," Mr Tkachev was quoted as saying by Russia's Interfax news agency.
"The damage is so great that it's hard to assess. It can be equated with an ecological catastrophe," the governor said.
Oil-soaked birds have been seen struggling in the polluted water, and a number of them have been found dead on the sandy shores.
Others have been seen hopping weakly along the beaches, weighed down by a thick coating of fuel oil.
Hundreds of Russian soldiers have deployed to clean up the spill, but the operation is being hampered by stormy weather.
Soil-excavating vehicles have been sent to clear affected beaches around the Russian port of Kavkaz.
Helicopter and ships equipped with tackling the oil spill at sea have been hampered by more stormy weather.
The prime ministers of Russia and Ukraine are due to visit the region later on Tuesday to discuss the emergency aid plan.
Russian environmentalist Vladimir Slivyak told the AFP news agency the tanker accident was a "very serious environmental disaster".
The heavy oil was sinking to the seabed and could take years to clean up, he said.
Russian prosecutors say they are investigating whether the ships' captains ignored warnings of the approaching storm.