Cyanobacteria (blue-green algae) are natural organisms that are present in most lakes. Certain conditions – low water levels, limited water circulation, increased heat and light, among other factors – can cause cyanobacteria to bloom and, in some cases, release toxins. The most common cyanobacteria toxins are Anatoxin-A, a neurotoxin, and Microcystin, which affects the liver. Scientists do not know what causes the cyanobacteria to become toxic.
The Park District had never before seen toxic algae blooms in its lakes, but in 2014, recorded three, most likely due to the drought. The first and third toxic blooms were in Lake Temescal in Oakland, both blooms resulted in its closure for a total of about nine weeks over the summer and fall, and a second bloom was discovered in September in Lake Chabot and still remains.
Exposure to toxic algae, either through ingestion or skin contact, can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal problems or, at high doses, serious illness or death, according to the California Department of Public Health. Several dog deaths around the state have been attributed to toxic algae poisoning in the past two years.
Blooms usually run their course and dissipate in a week or two, but rainstorms and cold temperatures can speed up the process. At Lake Temescal, the Park District used an organic chemical called GreenClean to control the algae. The chemical is safe for water used for drinking, swimming, and fishing, and does not harm other aquatic life. The District has only used the chemical in Lake Chabot at the Marina because the lake is very large in size. The water in Lake Chabot is under the jurisdiction of the East Bay Municipal Utility District.
Swimming – by dogs or people – is not allowed at Lake Chabot. Several signs at the lake warn visitors to stay out of the water due to the algae, rinse skin with tap water after contact, and keep pets away from the water. Fish should be rinsed in tap water and the guts discarded.