The concentration of cesium-137 exceeded the EU maximum recommended level in 20 percent of fish and more than half of the mushrooms tested in 2005 by the Radiation and Nuclear Safety Authority and Finnish Food Safety Authority Evira.
The tests were conducted in the lakes and region around Vammala, 230 kilometers (145 miles) northwest of Helsinki in southwestern Finland -- the Finnish area most affected by the fallout from the Chernobyl disaster on April 26, 1986.
Radioactivity levels reached nearly three and a half times the maximum recommended level in fish and up to nine times the maximum in mushrooms, with significant variations depending on where the tests were carried out and other factors.
Seventeen percent of fish also had elevated levels of mercury.
Finnish authorities recommend consumers eat lake fish no more than once or twice a month -- expectant mothers are advised to stay away from pike entirely during their pregnancy -- and to wash mushrooms well before eating.