About the Lake

Clear Lake attracts visitors – anglers, hikers, swimmers, and nature enthusiasts alike – from around California and across the world. The Clear Lake basin has been occupied by the Elem Native Americans for over 11,000 years, as they have thrived on the abundant fish, game and water birds that call this lake home.

Clear Lake is the largest freshwater lake in California and the oldest lake in the northern hemisphere. It is also the home of an immense source for blue green algae, a primary foundation of the organic material, and also one of the oldest and most simple food sources on the planet, and most importantly, the beginning of the food chain.

The lake lies about 100 miles northeast of San Francisco, adjacent to the extinct volcano, Mt. Konocti.  With only an average depth of twenty-three feet, the lake has a sediment level that extends to around four miles deep.  The sediment has been accumulating for some four million years of yearly layer upon layer of blue green algae growth, along with natural sediment runoff from the hills and mountains.  Like a giant circulatory system, its aquifers feed into streams and rivers that eventually flow into the Sacramento Valley, Napa Valley and the San Francisco Bay.  

There is however, a threat that jeopardizes this system with the same issue that affected the Roman Empire at the time of its fall - heavy metals.  Historians profess that the people of Ancient Rome suffered lead exposure from pots and other vessels, which in turn, concertedly contributed to the fall of the Roman Empire.  “Mad as a Hatter”, had its roots from the effects of mercury in the old hat making industry. Unintentional though it was then, the evidence of heavy metal’s damaging effects on people is now widely accepted and we can no longer claim ignorance.  

The primary source of Clear Lake’s bio-accumulative pollution is the abandoned Sulphur Bank Mercury Mine. For more information about this mine and the toxins it is leaching into some of California’s major waterways, read more about What’s At Stake.