The federal water master in Reno says the lake will probably hit its top, allowable level this summer. In the meantime, the water master will instruct the gate-keeper to open or close one or more of the 17 gates in the dam in Tahoe City.

This is done to control the flow of water down the Truckee River as well as the height of the lake. If the lake gets too high, too fast, all 17 gates will have to be opened, which can cause flooding downstream. All 17 gates were opened wide twice in 1996. The lake was at it highest in the century in July 1907 when it reached 6,231.26 feet. It was lowest in November 1992 when it shrunk to 6,220.26 feet.

Currently the dam has one gate open.



By law, the lake surface is managed to remain in the range between a low of 6,223 feet (the lake's natural rim) and a maximum allowable height of 6,229.1 feet, which was established by a Federal Court. The 6.1 feet of difference between high and low is a "reservoir" of water sitting at the top of Lake Tahoe for downstream users. There are 744,600 acre-feet in the 6.1-foot reservoir. An acre-foot is enough water to cover one acre to a depth of one foot--325,851 gallons.

The gage used to monitor the lake level is located on the U.S. Coast Guard pier in Lake Forest, just east of Tahoe City. The Daily Gage Height on the left axis displays the distance above 6,220 feet in altitude. So if the Gage Height reads 6.56 feet, the actual altitude of the Lake Tahoe surface is 6,226.56 feet.



On the current graph above, the line shows the level of the lake moved from 6.56 to 7.06 This is a 0.5-foot change, or six inches. In terms of altitude, the lake moved up from 6,226.56 (6,220 base altitude + 6.56 on gage = 6,226.56 feet) to 6,227.06 feet. You can see the graph yourself any time at http://waterdata.usgs.gov/ca/nwis/dv/?site_no=10337000&agency_cd=USGS