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Grand Teton National Park Report

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Beginning in 1978, the water level of Jackson Lake, Grand Teton National Park, Wyoming, was lowered first from 2064.5m (normal pool) to between 2060.3m-2061.8m, and then in 1985 to 2057.2m. The purpose of these drawdowns was to facilitate repair and modification of the Jackson Lake dam. In 1989, repair was completed and the reservoir was allowed to fill back to the normal pool elevation of 2064.5m Because of impacts to the littoral habitat in Jackson Lake caused by restoration of the dam at the Snake River outlet, the status of the aquatic plant community was assessed in August, 1989, to follow up to investigations conducted in 1983 (prior to reconstruction) and 1985 (immediately following drawdown to 2055.4m) by Brewer (1986). This report summarizes findings from the 1989 study on impacts to the littoral macrophyte community caused by the repair-related drawdowns. A detailed report assessing current physical and biological conditions in Jackson Lake was submitted to the U.S. Fish and Wildlife Service in October (Brewer, 1989).