"The water is clean. The fish is safe to eat. The beaches are safe to play on," Godlewski said.
Lake Roosevelt is a 150-mile reservoir created by Grand Coulee Dam on the Columbia River. The popular recreation site is used by more than 1 million people per year.
In September, Teck Metals said in court for the first time that some of the pollution it dumped into the river between 1896 and 1995 flowed into the United States, and some hazardous substances were released into the U.S. environment.
The statement seemed to eliminate the need for a costly trial on the source of the pollution.
Much of the pollution is a fine black sand known as slag that washed downstream onto beaches at the lake where people camp and swim.
"Teck knew its disposal of hazardous waste into the (river) was likely to cause harm," the judge wrote in his ruling. "It was told by the Canadian government that its slag was toxic to fish and leached hazardous metals."
The Colville tribes petitioned the U.S. Environmental Protection Agency a decade ago to assess contamination in the reservoir. In 2003, the EPA decided Teck was subject to the U.S. Superfund law, demanded the company pay for studies to determine the extent of the pollution, and clean it up.
Teck objected and the tribes filed suit in 2004 to force the company to comply. The state then joined the case.
However, Teck did agree in 2006 to perform a major study of pollution in the lake, under the direction of the EPA. The company has spent more than $55 million on the study, scheduled for completion in 2015.
Godlewski said no decisions can be made on the extent of a cleanup, and its cost, until the study is concluded.
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