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Brownish-red water in Oakland's Lake Merritt could be harmful algal bloom

Walkers at Lake Merritt react to algae bloom, murky 'snot' color
People walking around Lake Merritt react to algae bloom, murky 'snot' color 02:01

OAKLAND (BCN/KPIX) – Some areas of Lake Merritt are changing color, raising the concern of toxic algae in the water.

A complaint about brownish-red water in the lake last week led Oakland Public Works to inspect the water for a potential harmful algal bloom. 

The complaint came from a resident near the 1200 to 1400 blocks of Lakeshore Avenue, the same area where testing found low levels of contaminants associated with harmful algal bloom earlier this year. 

Lake Merritt in Oakland
Lake Merritt in Oakland. CBS

Residents who enjoy walking around Lake Merritt say they've noticed a significant change in the water over the last month.

"It's a lot more murkier now. It's just gross man," said DJ Daniels.

"Just looks murkier and we were just talking, it looks like a snot pile," added Cara Spangler. "I've never seen anything like it before actually."

Oakland Public Works detected low levels of Cyanobacteria in May which is associated with harmful algal bloom. Now the problem maybe worsening, leading OPW to conduct additional inspection. 

The advice for now is to have everyone, especially kids and pets to not get close to the water. 

"I just try to stay as far away from the water as I can," said Daniels.

OPW says more human and animal waste along with stagnant water and high temperatures are contributing to the problem. The City is asking residents to avoid over-irrigation and to keep the lake clean by limiting trash. 

Spangler agrees.

"More education and awareness on why it's important to keep the lake clean and what it does for all of us. It definitely has become more part of the community and the culture here," said Spangler.

OPW is in the process of submitting a report to the San Francisco Bay Regional Water Quality Control Board.

It expects more testing will be done in the coming weeks and will provide additional warnings if needed.

Harmful algal bloom is generally caused by an increase in nutrients like nitrogen and phosphorus from fertilizers and human or animal waste in the water. It can also be caused by low water flows and increased intensity and duration of sunlight. 

Research suggests that rising temperatures and changing precipitation patterns caused by climate change are a catalyst for cyanobacterial growth. 

Staff also note that algae is a regularly occurring organism in Lake Merritt. Most summers, the city of Oakland employs an algae skimmer to harvest algae from the lake.

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