With Lake Tahoe's water level nearing the natural rim, water authorities are hoping for record-breaking precipitation to bring the level up.
"We desperately need a big winter and a big snowpack to bring Lake Tahoe back up again," said Federal Water Master Garry Stone.
When the water in Lake Tahoe nears the natural rim, at 6,223 feet, water flows more slowly into the Truckee River.
At midweek the lake measured 6,223.25. Under normal conditions, the flow into the Truckee is about 250 cubic feet per second. The current rate is about 12 cubic feet per second, Stone said. If the lake level drops below the natural rim no more water will flow into the Truckee.
"We can't get any more water out of it," Stone said. "It's like a bathtub, we do not have the ability to release water through the natural rim."
Water from Boca Reservoir and smaller natural streams will continue to flow through the Truckee.
Stone said there is enough water in Boca to supply the river until sometime in December.
Stone said the region needs a winter with three or four times the average snowpack to bring the river above the natural rim and to an adequate level.
"It's a very tenuous situation," he said.
The average winter precipitation for the Tahoe area is 31.77 inches, said Jim Ashby, climatologist with the Western Regional Climate center. In the past 100 years, only two winters have topped 60 inches of precipitation, in 1981-1982 with 64.25 inches and 1994-1995 with 61.21 inches.
"Those winters are pretty unusual," he said.
A snowpack large enough to keep the lake safely above the rim would be unusual and unprecedented, said Dan Greenlee, a Water Supply Specialist with the Natural Resources Conservation Service.
"We'd be buried from here until next July Fourth," he said.
Although this fall has been mild, anything could happen this winter, Greenlee said.
"It's not untypical to have no snow at these sites," he said. "You can't tell what's going to happen at this point in the year."