AB or HAB?

Algal bloom in North Basin

The waters on the east side of the park have been covered in recent days with a bloom of green algae. Sometimes they form a blanket, as in the video above. At other times the algae show up in ragged patches, sometimes with bubbles, see photo below. Is this an event of little concern, a benign Algal Bloom (AB). Or is it a biochemical explosion of toxic cyanobacteria that will clog fish gills, poison wildlife, and harm humans — a Harmful Algal Bloom (HAB)?

I’ve learned that the East Bay Regional Park system regularly tests lake waters in its domain, and that the Oakland Parks system uses a contractor that tests waters there, notably at Lake Merritt. The Berkeley Parks and Waterfront Department has similar capabilities, given the recurring algal bloom problem in nearby Aquatic Park. The City of Berkeley Division of Environmental Health performs the Aquatic Park water testing.

Thursday morning’s northerly winds and rising tide dredged up the bottom and turned the water brown. But as the day warmed up and the winds shifted west, the silt settled and the green began to resurface. We’re not done with the algae. Until there’s a water test and we know whether it’s just a benign AB or a toxic HAB, it’s prudent to be cautious: avoid water contact, don’t eat fish caught in it.

Algal bloom in North Basin

More about ABs and HABs: Wikipedia Primer

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