OAKLAND (CBS SF) — Three dogs have died from poisoning after drinking the water from Lake Chabot. The man-made lake straddles Oakland and unincorporated Castro Valley.

The lake has had a poisonous algae bloom since September 2014. Cyanobacteria, also known as blue-green algae, is harmful to humans and animals.

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The most recent death was reported this week. Two other dogs died in December.

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Park and municipal officials have issued an urgent warning for dog owners to keep their pets away from the water at Lake Chabot.

East Bay Regional Park and East Bay Municipal Utility District workers spent Saturday posting signs along lake trails warning about the algae problem and its toxicity to animals and humans. Swimming and wading is not allowed.

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Algae blooms normally happen in late summer, not during the winter. Officials believe unseasonably warm temperatures and drought conditions are exacerbating the problem.