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Water : Supply Sources

- Reservoir Levels

The City of San Luis Obispo has adopted a multi-source water supply strategy and obtains water from five sources: Salinas Reservoir (Santa Margarita Lake), Whale Rock Reservoir, Nacimiento Reservoir, ground water, and recycled water

Whale Rock Lake.
Whale Rock Reservoir

City’s Investment in Multi-Source Water Supply

Providing Drought Dividends

Despite the Govenor’s recent declaration of a drought emergency and the desperate stories of State water shortages, the City’s local water supply remains reliable and secure. Assuming historical worst case drought conditions and January 2014 reservoir storage levels, water projection modeling estimates about 7.5 years of water currently available (with the last three of those years being a period where mandatory conservation actions would occur).

While our memories can quickly fade, the 1987-1991 drought had a profound effect on San Luis Obispo and those who experienced it can vividly recall the impacts. The subsequent decisions made and actions taken by City Council, community members, and staff to secure reliable water resources for the City are paying dividends.

Investment in a multi-source water supply allows for responsible use even following the direst year on record. As with any precious resource, it should be used wisely and efficiently.

The City has four primary water supply sources including Whale Rock Reservoir, Salinas Reservoir, Nacimiento Reservoir, and recycled water (for irrigation), with groundwater serving as a fifth supplemental source.
Utilities Services Section is available to assist with questions regarding drought, irrigation practices, and water-wise landscaping. Please contact Utilities Services Manager Ron Munds at

Salinas Reservoir

The Salinas Dam was built in 1941 by the War Department to supply water to Camp San Luis Obispo and, secondarily, to meet the water needs of the City. The Salinas Reservoir (Santa Margarita Lake) captures water from a 112 square mile watershed and can currently store up to 23,843 acre-feet.Santa Margarita Lake. In 1947, the Salinas Dam and delivery system was transferred from the regular Army to the U.S. Army Corps of Engineers. Since the late 40's or early 50's, the San Luis Obispo County Flood Control and Water Conservation District has operated this water supply for the City under a lease from the U.S. Army Corps of Engineers. Water from the reservoir is pumped through the Cuesta Tunnel (a one mile long tunnel through the mountains of the Cuesta Ridge) and then flows by gravity to the City’s Water Treatment Plant on Stenner Creek Road.

The City has water rights to store up to 45,000 acre feet. The original design of the dam included a gate in the spillway to increase the storage capacity.

Whale Rock Reservoir

The Whale Rock Reservoir is a 40,662 acre foot reservoir created by the construction an earthen dam on Old Creek near the town of Cayucos. TheWhale Rock Lake. dam was designed and constructed by the State Department of Water Resources beginning in October 1958 and completed in April 1961, to provide water to the City of San Luis Obispo, Cal Poly State University and California Men’s Colony. The Whale Rock Dam captures water from a 20.3  square mile watershed and water is delivered to the three agencies through 17.6 miles of 30-inch pipeline and two pumping stations.

Nacimiento Reservoir

The Nacimiento Reservoir provides flood protection and is a source of supply for groundwater recharge for the Salinas Valley. It is owned and operated by the Monterey County Water Resources Agency. Since 1959, the San Luis Obispo County Flood Control and Water Conservation District has had an entitlement to 17,500 acre-feet per year (AFY) of water from the reservoir for use in San Luis Obispo County. Approximately 1,750 AFY have been designated for uses around the lake, leaving 15,750 AFY for allocation to other areas within the County of San Luis Obispo.

The County began construction in 2007 on a 45-mile pipeline project to deliver water from the Nacimiento Reservoir to five participating agencies and cities. The City has a contractual entitlement to 3,380 AFY of water from the project. The construction of the pipeline and delivery facilities was substantially completed in December 2010 and water deliveries to the City began in January 2011.

Q: Is there Mercury in Nacimiento Water?

A: Click here for a pdf fact sheet.

Ground Water

One well currently supplies water for domestic use. Two wells supply water for irrigating the City golf course, and one well at the Corporation Yard is used for construction purposes. The one domestic well is producing approximately 10 acre feet per month which is approximately 2% of the total City water use. The groundwater basin is relatively small and recharges very quickly following normal rainfall periods, but it also lowers relatively quickly following the end of the rainy season. Extensive use of groundwater sustained the City through the drought of 1986-1991. However the City’s two largest producing wells, the Auto Parkway and Denny’s wells, were shut down when elevated nitrate levels were detected. This loss meant the City could not rely on groundwater for future drought protection.

Recycled Water

Recycled water is highly treated wastewater approved for reuse by the California Department of Public Health for a variety of applications, including landscape irrigation and construction dust control. Completed in 2006, the Water Reuse Project created the first new source of water for the City since 1961 following construction of Whale Rock Dam. The Project resulted in improvements at the City’s Water Reclamation Facility and an initial eight miles of distribution pipeline. The City’s first delivery of recycled water took place in 2006. The City estimates demand exists for approximately 1,000 acre feet of recycled water for landscape irrigation and other approved uses.

For more info about City of San Luis Obispo's recycled water, click here.

Recreation at the Reservoirs

Santa Margarita LakeRecreation facilities at Santa Margarita Lake are operated by the County of San Luis Obispo as a County Park and provide opportunities for boating, fishing, picnicking and camping. No body contact (swimming, waterskiing, etc.) is allowed in the lake because it is a domestic water supply reservoir. For more information call (805) 438-5485, or click here.

Whale Rock Reservoir has limited access to the south shore for hiking and fishing from the shore. A daily fee of $1.00 for hiking or $2.00 for fishing per person is collected to partially recover the costs of patrolling these areas. The fish population includes steelhead, catfish, blue gill, and Sacramento suckers.  Access to the Whale Rock Reservoir shoreline for fishing begins the last Saturday in April and extends through November 15th.

Recreation facilities at Nacimiento Lake are operated by the County of Monterey Parks Department. For more information concerning recreation activities at Nacimiento Lake visit their website here.

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