Residents in the Vaucluse, a popular southern French tourist destination, were banned yesterday from drinking well-water or swimming or fishing in two rivers after a uranium leak from one of France's nuclear power plants.

Nuclear officials yesterday revised down the amount of untreated liquid uranium that spilled from the Tricastin nuclear power centre in Bollene, saying it was limited to 75kg and ranked grade one on the one-to-seven scale of nuclear accidents. But the spillage of waste material containing uranium in the picturesque area of Provence, 30 miles from Avignon, which is currently hosting an arts festival, embarrassed the government.

Nicolas Sarkozy has prioritised exporting nuclear expertise worldwide, including to Britain. Nuclear power comprises 87% of France's electricity production, but yesterday anti-nuclear groups renewed their criticisms of the nuclear power policy.

The leak occurred when a tank was being cleaned between Monday night and Tuesday morning but was not detected until yesterday. Around 30 cubic metres of liquid containing uranium, which was not enriched, leaked out of a tank. Of this, 18 cubic metres poured on to the ground and into the nearby Gaffiere and Lauzon rivers, which flow into the Rhone. The plant has been operational since 1975.

Vaucluse authorities banned drinking well-water, fishing and eating fish from the rivers as well as swimming and water sports and irrigating crops with potentially contaminated water. One swimmer among 100 bathers asked to immediately vacate a local lake said it was as if there had been sharks in it.

Officials from the Socatri safety agency, a subsidiary of nuclear giant Areva, said groundwater, wells and rivers had shown no effects yesterday. The nuclear safety authority said radioactive levels detected in rivers and lakes in the region were decreasing.

The prefecture of Vaucluse said the leaked uranium should only be found in very small quantities and the risk was low but the ban on drinking, fishing and swimming would continue.

Germany's Social Democrat environment minister, Michael Müller, whose party is opposed to nuclear energy, said yesterday that the incident should not be taken lightly. "It's no trifle when active uranium penetrates the soil," he told Agence France Presse.

The French environmental group, the Committee for Independent Research and Information on Radioactivity, said that the radioactivity released into the environment was at least 100 times higher than the fixed limit for that site for the entire year.

Greenpeace International nuclear campaigner, Aslihan Tumer, said: "Given the restrictions on the consumption and use of water in the area, it is clear that the leak poses a risk to the local population and to the environment."