|Location||Marin County, California|
|Primary inflows||Nicasio Creek|
|Primary outflows||Nicasio Creek|
|Basin countries||United States|
|Surface area||845 acres (3.42 km2)|
|Water volume||22,400 acre·ft (27,600,000 m3)|
|Surface elevation||144 ft (44 m)|
Nicasio Reservoir is a shallow, artificial reservoir in the Nicasio Valley region of Marin County, California, United States. It covers 845 acres (3.42 km2) and sits in a 35.9 square miles (93 km2) drainage basin. It was created by the construction of Seeger Dam on the Nicasio Creek in 1961. Seeger Dam is a 115-foot (35 m) tall, 400-foot (120 m) long earthen dam owned by the Marin Municipal Water District.
The construction in the dam aroused much controversy among longtime residents of the area. The Water District forced the displacement of many farms, including the McIsaac family farm and the Tomasini Ranch, on which the majority of the reservoir sits. The controversy stems from the fact the water from the reservoir is rarely used by the Water District, that the broad and shallow nature of the reservoir leads to quick evaporation, and that the dam has blocked valuable spawning areas for endangered coho salmon and threatened steelhead trout. Construction of Seeger Dam wiped out the salmon population in Nicasio Creek. The District briefly attempted to trap salmon below the dam and transport them by truck further up Nicasio Creek and Halleck Creek. However, the effort proved unsuccessful.
- "Dams Within the Jurisdiction of the State of California" (PDF). Retrieved 2008-01-17.
- U.S. Geological Survey Geographic Names Information System: Nicasio Reservoir
- Resneck, Jacob (October 28, 2004). "Nicasio History Revealed by Low Reservoir". Point Reyes Light.
- "North-Central California Coast Recovery Program 5-Year Review: Summary and Evaluation of California Coastal Chinook Salmon ESU, Central California Coast Coho Salmon ESU" (PDF). National Oceanic and Atmospheric Administration. 2011. Retrieved 2013-12-03.
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- "Lontra canadensis brevipilosus". Museum of Vertebrate Zoology. 2008-01-29. Retrieved 2011-05-23.