Thousands of trout were killed in Switzerland after technical trouble at a hydroelectric dam stemmed the water flow in a national park, the Swiss news agency ATS reported. The incident occurred Saturday at the Punt da Gall dam in the Graubuenden region in eastern Switzerland, ATS quoted the power firm Engadiner Kraftwerk and the Swiss National Park as saying. Earlier Saturday, park rangers raised the alarm after noticing that the water level in the River Spoel had dropped dramatically. As a result, officials at the dam opted to open a duct to resolve the problem. But that decision proved to be a major error. It sent a wave of sediment spiralling downstream, killing the trout and other aquatic wildlife along a six-kilometre (four-mile) stretch of river.