Whose water is it? Lake Tahoe water levels dropping quickly as demand increases

LAKE TAHOE, Calif./Nev. - Those watching the level of Lake Tahoe know it is dropping quickly, and it's not just because of a lack of snowfall this year and another year of drought.

Understanding why the lake drops, and who causes it to drop (yes, there is a person - the watermaster), is key to knowing why the lake should be at its natural rim of 6,223 feet above sea level by the beginning of August. As of June 8 the lake is two feet above that rim.

The surface of Lake Tahoe is 22 miles long and 12 miles wide and 191 square miles. The shoreline length is 75 miles and with an average depth of 1,000 feet, there is a lot of water in this jewel of the Sierra, 36.15 cubic miles or 39,000,000,000 (trillion) gallons of it, in fact.

So much surface water that 360,000 acre-feet of water evaporate from Lake Tahoe in an average year - enough water to flood 360,000 acres of land to a depth of one foot or supply water to about 360-720 families for a full year (California households use between one-half and one acre-foot of water per year for indoor and outdoor use).

The lake fills every year from snow and precipitation that falls on its surface and comes through the streams in the Tahoe Basin watershed.

Water is let out at the one outlet at the dam at Tahoe City which is under the control of the Federal Watermaster. But how much, and why?

Every gallon that leaves Tahoe is spoken for and is divided up through court decrees with input through a consortium of sorts of those who have a piece of the water pot.

The Truckee River Operating Agreement (TROA) was implemented in 2015 that provides the management of the water and summarizes the water and hydrologic data needed to send the water from Tahoe on its way to those downstream. TROA meetings are held monthly with all partners, the Pyramid Lake Paiute Tribe, State of California, State of Nevada, Washoe County (Reno, Sparks), City of Fernley, Truckee Meadows Water Authority, and the federal government. They work out the water use for the region.

Things changed in the drought year 2015 as water recipients didn't want water stranded in Lake Tahoe since once the lake hits its natural rim, the dam won't flow. Prior to TROA, Tahoe water was stored for Nevada, and now California can store it in Tahoe. TROA was the culmination of decades of "deliberative and careful water resource planning designed to address concerns over future water supply. TROA replaces the rigid and inflexible water management system for the Truckee River," according to the Truckee Meadows Water Authority 20-year water plan. It replaced the decades-old court decrees originally designed to serve agriculture, small hydroelectric plants, now defunct paper mills, and a small, rural community. Now they can adapt to future variability of climatic, hydrologic, and economic conditions while taking advantage of unused storage space in federal reservoirs.

2021 is a drought year, and all demand for water is coming from Lake Tahoe, according to Chief Deputy Water Master Dave Wathen. Reservoir levels are dropping across California and those who have rights to Tahoe water want it now before it's too late.

Parties of TROA can get credit for water they don't use in a year, and there has been accumulated water credit in Lake Tahoe over the last few years. Wathen said they don't want their water trapped in the Lake Tahoe Basin when the dam closes and they want it now. Plus, they'd like it before evaporation takes what they can use. More water is lost to evaporation that is released at the dam.

Release at the dam will remain high. Full demand is 500 cubic sure feet (CSF) per second and the release has been averaging at closer to 400 CSF. There will also be plenty of water left in Tahoe when you think about the average depth is 1,000 feet and the dam not functioning when the lake is below the natural rim.

There is not much water in other storage areas like Boca and Prosser reservoir. Wathen said a lot with credits want to move them to Boca and Prosser for the future so they don't have to only get water when the dam flow allows it.

The water rights through TROA are scheduled to change all the time just as the amount of water available changes. Wathen said everyone works together under an operating agreement where people have a right to establish credits and they also share expectations and work on the plans. In California, there is also another monthly meeting of the Truckee River Watershed Council that covers local interests including recreation, fisheries, and the environment through multi-agency collaboration.