Decades of mining have slopped about 72 million tonnes of lead, zinc and other metal wastes into the Coeur d:lene lake in Idaho state in the US. Now, representatives of the Coeur d:lene tribe and the environmentalist group, Sierra Club, have urged the Congress and the Clinton administration to fund a $1-billion restoration effort. Although the heavy metals entombed in the sediment pose no immediate threat, oxygen depletion near the bed presents a daunting cleanup challenge. Sierra Club representative Kathryn Hohmann said the situation is "a time bomb ticking on the land".