Waste containing unenriched uranium has leaked into two rivers from a nuclear plant in southern France.
Officials banned people in three nearby towns from fishing, using water from wells, swimming in the rivers or using river water on their crops.
The accident happened at the Tricastin nuclear site at Bollene, some 40km (25 miles) from the city of Avignon.
The French nuclear safety agency said the substance was toxic but the risk to human health was slight.
Uranium concentrations in the Gaffiere river were initially about 1,000 times higher than normal levels but were falling rapidly, spokeswoman Evangelia Petit said.
Some 30,000l (7,925 gallons) of solution containing 12g of uranium per litre spilled from an overflowing reservoir at the facility - which handles liquids contaminated by uranium - into the ground and into the Gaffiere and Lauzon rivers.
Anti-nuclear campaign group Abandon Nuclear Power said it thought the authorities were underplaying the danger posed by the nuclear waste leak.
"It is impossible that such a spill, containing uranium, does not have important consequences for the environment and for health," it said.
France is one of the world's most nuclear-dependent countries, with 80% of its electricity coming from nuclear power.