O.C. Fisher Reservoir Depleted, Nasworthy Water Sent Downstream

O.C. Fisher Reservoir, which had been supplementing the City of San Angelo’s water supply, has been depleted. At the same time, the City is increasing the amount of water it must release from Lake Nasworthy to downstream water rights holders, as required by the Concho Water Master Program.

The convergence of Fisher’s depletion and the necessary release of water downstream will dramatically affect the level of Lake Nasworthy, which is currently at 70 percent of its capacity. The City’s Water Utilities Department continues to monitor the lake’s level to advise citizens who live around the lake and those who use the reservoir for recreational activities of the changing conditions.

Without replenishing rainfall, Nasworthy’s level will continue to decline. To date this year, San Angelo has recorded only 0.06 inches of rainfall compared to 1.43 inches last year and a year-to-date average of 1.01 inches.

During the fall and winter months, Nasworthy’s decline has been minimal – about 1 percentage point of its capacity per week. Water usage is lowest in the winter – about 9 million gallons per day – as are evaporation rates. Summertime usage can be two to three times that amount, depending upon the watering restrictions in place. Without adequate rainfall, Lake Nasworthy’s water level will see even more dramatic changes in the spring and summer.

The City is currently relying upon O.H. Ivie Reservoir for most of its raw water needs. Ivie is at 13 percent of its capacity. San Angelo has less than 15 months of available water supply, assuming no rainfall or runoff during that span. That supply will be supplemented this fall by up to 9 million gallons from the Hickory Aquifer. A facility to treat the Hickory’s groundwater is under construction.

The City urges lakefront homeowners to monitor the lake for changing conditions.