As you may be aware, a large algae bloom is currently occurring in Mountain Lake. Annual summertime algae blooms occur in many water bodies around California and historically at Mountain Lake. Blooms are typically caused by a combination of excess nutrients, warmer temperatures and ample sunlight, and may last several months.
We expected a significant bloom at Mountain Lake this summer due to the recent above average temperatures and the amount of suspended nutrients in the water resulting from the recent dredging of the lake bottom. The current bloom is expected to dissipate in the fall. However we recently identified a type of Blue-Green algae (Microscystis aeruginosa), which has the potential to have adverse effects on human and animal health, in the lake. Out of an abundance of caution and to ensure the safety of park visitors and their pets, we are going to restrict access to the beach until this algae bloom subsides. Trust staff has temporarily closed off the access to the Mountain Lake beach, and installed public safety signage.
As you know, we are in the midst of ongoing work on a number of restoration projects at the lake including installation of an aeration system, eradication of invasive fish, replanting of submerged aquatic vegetation, and reintroductions of native plant and animal species. All of these measures will improve the health of the lake and help reduce the likelihood of large algae blooms in the future.
We will keep you informed on the safety of the lake as conditions progress and notify you when the beach is ready to reopen. If you have questions, please contact the Presidio Trust at (415) 561-7602. Thank you for your ongoing interest and continued support of the restoration of Mountain Lake.