(KRON) — For weeks, the water in the Oakland and Alameda estuaries have been a murky, brown color.

The phenomenon is known as the ‘red tide’ blooms. A local environmental group is now testing the water to find out what’s behind it.

The environmental group, San Francisco Baykeeper, received reports at the end of July of serious water discoloration by houseboats. The Department of Public Health tested the water and found a harmful algal bloom.

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“Heterosigma akashiwo is a species known from around the world to cause what is commonly known as red tides. It’s been in Asia and Europe, throughout the East and West Coast,” said Ian Wren who is a scientist at San Francisco Baykeeper.

On Wednesday morning, a sample was taken by the San Francisco Estuary Institute.

Wren said blooms of this magnitude are relatively rare in the bay, particularly in the middle of summer. There can be numerous causes ranging from the ongoing drought to sewage treatment plants.

“Many of those treatment plants do not remove nutrients and that’s an essential building block for the algae that has really taken off in the estuary and throughout the central bay,” said Wren.

Experts said they are concerned about marine life.

“It is possible when this bloom dies you have a scenario when bacteria will consume the algae and suck a lot of the oxygen out of the water. You could have fish kills in shallower parts of the bay,” said Wren.

The algal bloom may not be as harmful to humans, but those exposed can suffer skin irritation and burning eyes.

“Thankfully, the city of Oakland opened up showers for us this week actually, so our rowers feel a lot safe. They are able to wash off after rowing,” said Caroline Cahill, program director of East Bay Rowing Club.

As for how long the water will stay this way, Wren and his team will continue monitoring and studying this phenomenon. So far, there is no official warning from the health department about the water, but the cities of Oakland, Alameda and Alameda County issued caution signs.