Toxic algae kills 2 dogs after swim in Napa County pond

Lake Temescal in Oakland was closed Wednesday because of an outbreak of toxic algae. On Friday, officials in Napa said they were advising swimmers to avoid ponds with similar outbreaks. Lake Temescal in Oakland was closed Wednesday because of an outbreak of toxic algae. On Friday, officials in Napa said they were advising swimmers to avoid ponds with similar outbreaks. Photo: Santiago Mejia, The Chronicle Buy photo Photo: Santiago Mejia, The Chronicle Image 1 of / 32 Caption Close Toxic algae kills 2 dogs after swim in Napa County pond 1 / 32 Back to Gallery

A growth of blue-green algae in a pond in southern Napa County killed two dogs that swam in the murky water this week, causing local officials Friday to issue a county-wide warning.

It’s the second reported outbreak of dangerous algae in the Bay Area in a week — Oakland’s Lake Temescal was closed following a similar outbreak that was the same color.

The warning by the county’s board of supervisors urges would-be swimmers to avoid ponds, rivers and streams in the area that may be contaminated with the toxic blue-green algae.

The two dogs swam in a pond off Huichica Creek, located where Milton Road ends, and may have drunk the water, the officials said. Signs posted in the area warned of the danger. Algae poisoning in people can cause serious injury to the liver, kidney and nervous system if the affected water is swallowed. Exposure requires immediate medical attention.

The algae blooms, which can be blue-green, white or brown in appearance, are caused by sitting or slow-moving water with an abundance of nutrients, officials said. And camping filters, purification tablet or boiling the water does not make it safe to drink.

Michael Bodley is a San Francisco Chronicle staff writer. Email: mbodley@sfchronicle.com. Twitter: @michael_bodley