It was created by the construction of Seeger Dam on the Nicasio Creek in 1961 (64 years ago) (1961).

[3] 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[4] and threatened steelhead trout.

[5] Construction of Seeger Dam wiped out the salmon population in Nicasio Creek.

[3] A river otter (Lontra canadensis) was collected by the Museum of Vertebrate Zoology at the southwest corner of Nicasio Reservoir in January 2008.

[citation needed] The California Office of Environmental Health Hazard Assessment (OEHHA) has developed a safe eating advisory for fish caught in Nicasio Reservoir based on levels of mercury or PCBs found in the fish species.