Upper Oso Reservoir Dam - Mission Viejo, CA
Posted by: 
DopeyDuck
N 33° 39.506 W 117° 37.801
11S E 441586 N 3724462
Owned by the Santa Margarita Water District, the Upper Oso Reservoir holds 1.3 billion gallons of recycled water thus conserving over a billion gallons of drinking water each year. It is one of the largest recycled water reservoir in Orange County.
Waymark Code: WM623A
Location: California, United States
Date Posted: 03/19/2009
Views: 9
The Upper Oso Reservoir (AKA Oso Lake) used to be open to bass fishing until the Boy Scouts started leasing the land. It is no longer open to the public. This reservoir was instrumental in fighting the Santiago fire in Oct 2007. The helicopters pulled a lot of water out of the lake, and as a result, the CO2 levels dropped significantly and it killed a lot of fish. Despite the fires and our recent drought conditions, the lake is finally starting to return to proper levels and the ecosystem is returning to normal.
According to the Sea and Sage Audubon Society (
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"Oso Reservoir is a fairly large body of freshwater in the Santa Ana foothills, managed by the Boy Scouts of America. This man-made lake is surrounded by remnant coastal sage scrub, and has patches of cattail marsh and, depending on its depth at any given moment, several small islands along the south shore. The main attraction here is waterbirds, and among those, the best are the large grebes of genus Aechmophorous,Western and Clark's. Both have been known to nest here, and in March, their weird frog-like cries echo among the hills as they meet in pairs to engage in their wild dancing, which features bizarre head-bobbing, neck-entwining and culminates in a mad side-by-side rush over the water's surface. It's a trip! The hills have Cactus Wrens and California Gnatcatchers along with Rufous-crowned Sparrows, while Least Bell's Vireos have nested in the lakeside willows."
In 2008, the water district held its Fiesta de Agua Family Fun Day at the lake. (
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The Specifications of the Upper Oso Dam are: (
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Upper Oso Dam is on Oso Creek in Orange County, California and is used for drinking water, drinking water, irrigation, recreation and recreation, among other things. Construction was completed in 1979. At normal levels it has a surface area of 115 acres. It is owned by Santa Margarita Water District.
Upper Oso is rock fill. Its height is 142 feet with a length of 800 feet. Normal storage is 3700 acre feet. It drains an area of 1.13 square miles.