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A bloom of blue green algae can be seen in the waters of Lake Temescal, Wednesday, July 23, 2014 in Oakland, Calif. For the first time, the algae has forced the closure of the swimming area, according to park officials, who said that the lake has always had blooms of the algae, but in the past, water testing revealed that it was non-toxic; not so this time. (D. Ross Cameron/Bay Area News Group)

OAKLAND -- One of the East Bay's most popular swimming holes is closed indefinitely because of a rare toxic algae bloom that poses health risks to people and dogs.

The East Bay Regional Park District closed public access to Lake Temescal last Thursday after tests found that a blue-green algae bloom contained high levels of the toxin microcystin, which can cause rashes, vomiting and flu-like symptoms.

The closure has disrupted several summer camps that use the lake. Park officials on Wednesday said they didn't know what caused the high level of toxicity and couldn't say when the lake would reopen for swimmers.

Outbreaks of thick green, oily algae typically occur each summer at the lake, which strides Highway 24 in the Oakland hills. But for the first time in recent memory, tests showed that the algae had toxin levels well above safety standards, said Hal MacLean, the park district's water management supervisor.

"You just don't know whether you are going to get the toxin or not," MacLean said. "You can't tell by looking at the scum on the water."

Lake Temescal is the only body of water in the park district to test positive for the toxin, which is released as the blue-green algae's cell walls break down. In fact, MacLean said, no park district property has had a toxic blue-green algae outbreak dating back at least to the 1970s.


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"The closing of water bodies because of blue-green algae blooms is pretty rare, period," said Geoff Schladow of the UC Davis Tahoe Environmental Research Center. Schladow said he was unaware of any increase in toxic algae blooms this year and that the lack of other blooms in the East Bay pointed to a local cause for the issue at Lake Temescal.

Toxic blue-green algae blooms are more common elsewhere in the state especially along the North Coast where toxic blooms have been blamed for the deaths of several dogs. For humans, the toxins generally cause skin irritation and digestive illness. More severe illnesses, including liver and nerve damage, can occur if the toxins enter drinking water supplies, according to state water officials.

Algae blooms are far more common in the summer when water temperatures rise and there is ample sunlight, said Dale Bowyer, senior water resource control engineer with the State Water Resources Control Board.

At Lake Temescal, the algae blooms typically last three days, but this outbreak is now it its third week, MacLean said. The park district is working with Alameda County health officials to test the water and determine when toxin levels are low enough to permit swimming again.

MacLean failed to provide the most recent testing results Wednesday, but said toxin levels were "well above" the hazard level set by the World Health Organization.

The park district is currently using a product to strip the lake of phosphorus, a mineral that nourishes the algae.

Another possible culprit could be reduced lawn watering from the drought, Schladow said. Reduced watering could result in less nitrogen from fertilizer running off into the lake, he said. While algae also need nitrogen to survive, blue-green algae, unlike other varieties, can absorb nitrogen from the air, so when nitrogen levels are lower in water, blue-green algae have a competitive advantage, he said.

The bloom means no swimming at the lake this weekend, and for camper's the park district's Junior Lifeguard Summer program, it has meant having to trek to other district lakes or switching to a land-based program.

Camp instructor Neil Wraske said the camp had to scrap its water rescue activities this week in favor of hikes and first-aid training.

"We're sill having a good time," he said. "But, yeah, it's a bit of a bummer."

Contact Matthew Artz at 510-208-6435.