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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 2064.5 m (normal pool) to somewhere between 2060-2061 m, and then in 1985 to 2057 m. 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 2065 m. 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 and 1990. Previous investigations conducted in 1983 (prior to reconstruction) and 1985 (immediately following drawdown to 2055 m) served as a baseline for comparisons. this report summarizes findings from the 1989 and 1990 studies on impacts to the littoral macrophyte community caused by the repair-related drawdowns. To evaluate the current status of the plant community in Jackson Lake, the following objectives were addressed during August, 1990: 1. Re-examine sites sampled in 1989; 2. Examine sites planted during the summers of 1989 and 1990 by the Bureau of Reclamation.