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Lake Temescal reopens after toxic scare

on September 4, 2014

One of the East Bay’s most popular swimming destinations reopened over the holiday weekend after a toxin-producing blue-green algae forced a closure earlier this summer. Experts are now saying the algae bloom that released the toxins is likely related to California’s dry spell. Lake Temescal, nestled in the Oakland hills between the Rockridge and Montclair neighborhoods, was bustling on Labor Day, despite the recent toxic scare. With the Indian summer setting in, Monday’s high temperatures led scores of swimmers to seek respite in the lake’s cool waters.

Algae blooms are a regular occurrence, but park officials say they took an unexpected turn this year. “We get the normal algae bloom in the summer,” said Vernon Jones, a park ranger at Temescal Lake. “It just got toxic this year, which has never happened before.”

Blooms of blue-green algae, or cyanobacteria, happen occasionally, but the blooms were particularly abundant this summer at Lake Temescal. Among cyanobacteria’s many species is one called Microcystis, which produces the toxin microcystin.Routine testing by the East Bay Regional Park District in July found the algae blooms contained the toxin, which can cause liver damage, nausea, diarrhea, vomiting, rashes and hives in humans. On July 14, the East Bay Regional Park District prohibited park patrons from any physical contact with the water. There were no reports of injuries or illnesses related to the algae since the July closure, but since then the park hasn’t seen many visitors.

While there have never been any reported human deaths as a result of contact with microcystis blooms, California’s Office of Environmental Health Hazard Assessment’s website says some animals have died from contact with it, including dogs, wildlife and livestock. Health Canada, Canada’s online health services information provider, says that animals are not more sensitive to the toxin than humans are, they’re just not as alert to the signs of potential danger, and therefore are more vulnerable to exposure.

Most blue-green algae blooms look like thick mats that float atop the water’s surface. They are mostly found in lakes, ponds and streams and usually give off a blue-green color, but can sometimes be just blue or green, or even purple. They also give off a distinct odor of decay.

Jones said he suspects the lack of rain and unusually warm winter this past year had something to do with toxic algae blooms. The lake’s culverts usually drain as it rains, but California’s current drought means old water isn’t getting flushed out. “If you don’t flush the toilet, dude, what happens? It starts to get nasty,” said Jones.

There is no consensus among scientists about the exact cause of these toxic algae blooms. But Kris Niyogi, professor of plant and microbial biology at UC Berkeley, agrees that climate can contribute to these biological changes. “It is possible that the weather pattern and/or specific environmental conditions at Lake Temescal this year could result in a different composition of the algal bloom in the lake,” Niyogi wrote in an email. “There are lots of algae and cyanobacteria that could potentially contribute to this bloom, and unfortunately the conditions this year must have favored cyanobacteria that can make microcystin.”

Matt Graul, the East Bay Regional Park District’s water resources manager, said the drought was “definitely a factor” because the decrease in runoff and rain flow into the lake creates shallower, more stagnant water, conditions that are more favorable for algae. He said warmer weather, still water and sunlight are the dominant factors in algae growth, but it’s the concentration of nutrients like phosphorus and nitrogen in low water levels that spur the production of blue-green algae. “We found high concentrations of phosphorus, which drive the blooming of algae,” said Graul.

Graul said the lake should not see more toxic algae for the rest of the year, but he isn’t ruling out outbreaks in subsequent summers. “It’s possible in the future, certainly, but we’re looking at ways to prevent this from occurring,” said Graul. “It could happen again next year.”

Water samples taken in late August, which were sent to the Animal Health & Food Safety Lab at UC Davis, found no detectable traces of the toxin so authorities reopened access to the lake just in time for the holiday weekend. The lake officially reopened on August 30 for recreational use.

Lake Temescal first opened as a public recreational area in 1936 and has become a popular urban oasis for locals. Prior to that, it was a reservoir supplying the then-small town of Oakland. Lake Temescal is one of a handful of recreational water bodies in Alameda County. Lake Merritt, Lake Chabot, Del Valle Regional Park and, of course, San Francisco Bay are some popular destinations for the public to enjoy the water. No other public water body in the county experienced a toxic algae bloom this summer, and there were no other closures.

Lake Temescal is open seven days a week from 5 am to 10 pm. Visit for more information.

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Photo by Basil D Soufi
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