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The water level of Grays Lake is controlled primarily by two factors: 1) precipitation and evaporation/transpiration balance, and 2) water level management at Clarks Cut by the Bureau of Indian Affairs. During spring, the lake level is high enough to flood the surrounding meadows. The lake is typically drawn down starting on 10 May to a standard level of 6386.0 ft by 24 June, and maintained at or near that level during the summer months, to supply water for irrigation, leaving only the bulrush and other deep marsh communities with standing water. At the lowest levels (6384.8 ft), most of the lake basin is dry but water remains by the north outlet and Beavertail control structures, in drainage canals, and in a few deeper natural ponds or openings. Only in very wet years is the summer water level at Grays Lake maintained such that standing water is available in the margins between the wet meadows and the tall emergent marsh. The first graph depicts the annual variability and median water levels recorded at Beavertail Point, 1979-2000, from April through October, summarized by 10-day periods. Other graphs show water level patterns for specific years.

Water levels for the Grays Lake basin have been most consistently monitored at Beavertail Point, which is centered on the south side of the basin. We have graphed patterns of water levels at Beavertail Point with available data for 1969-70 and 1979-1999.

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