Oakland Public Works received a complaint of brownish red water in Lake Merritt last week and are inspecting 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. 

Also known as cyanobacteria, algal blooms can produce toxins that are harmful to humans and animals. The brownish red color of the water reported by the resident indicates there could be a cyanobacteria bloom in the area. 

Public Works staff is inspecting the area and will submit a report to the San Francisco Bay Regional Water Quality Control Board. 

In May, Public Works staff posted warning signs along Lake Merritt in the same area after testing indicated that the lake water was contaminated. The signs alerted the public to keep children and pets away from the algae, scum and water.

Public Works staff say they will continue testing of the lake and will provide appropriate warnings to the public. 

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. 

Public Works staff request that property owners around Lake Merritt avoid over-irrigating their lawns to prevent excess nutrients from entering waterways. Food and food containers littered into Lake Merritt can also contribute to harmful algal bloom in the lake. 

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.