PARKS AND RECREATION/Lagoon preserves multi-purpose reservoir

Until the late 1990s, the Contra Costa (Calif.) Water District (CCWD) had multiple uses for its Contra Loma Reservoir, which stored an emergency supply of water for Contra Costa County and was open to the public for swimming, boating and fishing. Following state regulations that called for an end to the combined use of the reservoir, CCWD opened a swimming lagoon at the reservoir in May 2002 to preserve the quality of the water supply and the recreational facility for residents.

CCWD is an independent special district in the San Francisco Bay area that serves water to 450,000 people in central and eastern Contra Costa County. The Contra Loma Reservoir was built in 1967 by the U.S. Bureau of Reclamation (USBR) as part of the Contra Costa Canal to store water to meet peak demands and emergencies. The reservoir, located in Antioch, Calif., can store up to 2,532 acre-feet of water (827 million gallons) and has a surface area of 80 acres.

In 1968, CCWD, USBR and the East Bay Regional Park District (EBRPD) opened the reservoir to the public for recreation. For 30 years, residents visited the spot to swim, boat, fish and play water sports. However, in the 1990s, residents of several communities across the country — including those in Medford, Ore.; Grand Marais, Minn.; and Las Vegas — fell ill from Cryptosporidium in their water supplies. (Cryptosporidium is a pathogen that occurs in the feces of mammals and is recognized as causing disease in humans.)

Although CCWD treated the water from the Contra Loma Reservoir before it reached residents’ homes, the disease outbreaks demonstrated that water treatment might not protect residents from becoming ill. Therefore, keeping pathogens out of the water source became just as important as treating it. In 1997, the California Department of Health Services ordered CCWD to prohibit body contact recreation in the reservoir or to eliminate its use as a source of domestic water supply.

CCWD needed to keep the reservoir as a source for potable water, and EBRPD wanted to maintain the facility as a recreational spot for residents who have few other public places to swim in the area. As a solution, CCWD proposed building a swimming lagoon in the same area of the reservoir that had been roped off for swimmers. The lagoon would be separated from the reservoir by a berm to protect the drinking water.

Following negotiations with EBRPD about the design of the lagoon, CCWD started its construction in September 2001. The lagoon was built in the same location as the former swimming spot, providing approximately one acre of swimming area with 675,000 gallons of filtered and chlorinated water. The maximum depth is five feet, and it has a sandy bottom in the shallow wading area. Fishing, boating and windsurfing were allowed to continue in the reservoir with specific conditions, such as requiring windsurfers to shower before entering the water and to wear wet suits.

Construction of the Contra Loma Reservoir Lagoon cost $3 million and was paid for by CCWD. The lagoon opened on May 25, 2002, and is owned and operated by EBRPD.