By Alex Kirby
BBC News Online environment correspondent
Overfishing, pollution by the energy industry and the legacy of the Cold War all threaten the future of the Barents Sea, the UN Environment Programme says.
The waters of the Barents are cold and clean
A Unep report says the overexploitation of fish stocks is "the most alarming problem for the region at present".
It says the transport of oil and gas through the Barents Sea's Arctic waters is likely to increase six-fold by 2020.
Other threats Unep identifies include the storage of radioactive waste, and the introduction of new alien species.
Unep's warning comes in a report prepared by its Global International Waters Assessment division, and launched at the Offshore Northern Seas conference in the Norwegian city of Stavanger.
The report says the main reason for the various threats is an absence of long-term planning and legislation, with cod and haddock still overfished despite the existence of regulations and controls.
It says the Barents Sea, which lies north of Norway and Russia in the Arctic Ocean, is much cleaner than other European seas.
But pollution, it says, is the next most serious problem, because of the risks linked to the expansion of the hydrocarbon industries in the region.
Dr Klaus Toepfer, Unep's executive director, said: "The increased exploration activities for petroleum resources in the Barents Sea, the offshore developments and the shipping of oil and gas along the coasts represent significant potential threats."
The report says the development of the huge oil and gas deposits on Russia's Arctic shelf will increase oil transport to 40 million tonnes by 2020, increasing trans-Barents shipping by a factor of six.
It says the risk of accidental oil spills is expected to increase in the near future, and suggests ways to cut the risk of possible emergencies, including safety plans to prevent accidental oil spills, and contingency plans for responding to accidents.
Tanker movements are set for a huge increase
The region around the Russian port of Murmansk houses more radioactive waste than anywhere else in the world.
Unep says current levels of radioactivity are low and pose no threat to human health or the environment, but it calls for long-term strategies for the handling of stored nuclear material in the region.
The most striking example it cites of an alien species is the king crab, deliberately introduced to the Barents Sea in Soviet times.
Unep fears the crab may be competing with other species and damaging commercially important fish stocks.
It says another problem is the unintentional introduction of alien species in the ballast water of oil tankers, posing a serious threat to the economy of northern Norway as well as to coastal communities in Russia.