Tests have shown that some species of Baltic fish have too high levels of dioxin and the EU has called for a ban on sales of fish exceeding permitted levels from July 1.
Dioxins - cancer-causing toxic chemical compounds caused by burning plastic, fuel and rubbish - are hard to break down once they get into the food chain. They are also found in dairy products, meat and eggs.
The Baltic Sea has been exposed in the past century to heavy pollution, much of it deriving from industry in Russia's coastal cities of St Petersburg and Kaliningrad. Sweden is a driving force in efforts to clean up the sea and measures have been taken by the ex-Soviet states of Estonia, Latvia and Lithuania as they apply for membership of the EU. But the problems are far from solved and dioxin levels in fish remain a health risk in the region.
Among fish species with excessive dioxin levels is the Baltic herring. A smaller variety of the herring found in the North Sea, it is the main source of income for fishermen on Sweden's east coast. In 2001, the total herring take on Sweden's Baltic coast amounted to 11,700 tonnes, and Baltic herring is a staple of the region's food culture.