Del Valle Regional Park

Cyanobacteria (Blue-Green Algae)

Cyanobacteria (Blue-Green Algae) Information

Cyanobacteria (also called blue-green algae) are natural organisms that are present around the world in ocean and fresh water. Certain conditions – low water levels, limited water circulation, increased temperature and light, among other factors – can cause cyanobacteria to bloom and, in some cases, release toxins. Scientists do not know what causes the cyanobacteria to become toxic. We do know that these blooms are increasing around the world.

In 2014, the Park District had its first ever toxic algae bloom. Three incidents of toxic blooms were documented that year, most likely due to the drought.  Two toxic blooms occurred in Lake Temescal in Oakland. Both blooms resulted in lake closures to swimming for a total of about nine weeks over the summer and fall. Another bloom was observed in Lake Chabot.  Since 2014, the Park District has created a robust Harmful Algal Bloom (HAB) monitoring program to help ensure safe recreation in our lakes. To date, cyanobacteria blooms and toxins have been observed at all major Park District water bodies. 

The most common cyanobacteria toxins are Anatoxin-A, which impacts the nervous system, and Microcystin, which affects the liver.  Exposure to toxic algae, either through ingestion or skin contact, can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal problems or, at high doses, serious illness or death, according to the California Department of Public Health. In the past few years, several dog deaths in California have been attributed to toxic algae poisoning. To ensure fish are safe to eat throughout the Park District, annual fish tissue toxin tests are performed at major Park District lakes. Additionally, the new and improved Del Valle drinking water plant is tested regularly to ensure algal blooms do not impact drinking water sourced from the reservoir.  For more information on cyanobacteria please refer to the CCHABS website.

As the effects of climate change continue to escalate, we expect to see increased duration and frequency of harmful algal blooms. The Park District is implementing a diverse suite of management strategies to try and reduce the blooms and remediate the conditions causing the blooms. In July 2020, a hypolimnetic oxygenation system (HOS) was installed at Lake Anza in Tilden Regional Park. The goal of this system is to reduce the frequency and duration of toxic blooms by adding oxygen to the depths of Lake Anza. Oxygen binds essential nutrients making them unavailable for cyanobacterial growth. At Lake Temescal, application of a bonding agent have been used to limit and control HABs.

 

Media Coverage

Current Water Quality Conditions

Due to the drought and unusually warm weather conditions, toxic blooms of cyanobacteria (blue-green algae) and other water-quality issues are occurring more frequently in the East Bay Regional Park District and elsewhere. We monitor our lakes and shorelines regularly and post warnings and closures when appropriate. Here’s a current update of which lakes and shorelines are affected: 

Alert LevelParksDescription
Danger Advisory Posted
Water Quality Notice - Del Valle Reservoir

Cyanobacteria (blue-green algae) is present in the reservoir and a Danger/Closure Advisory is posted. NO SWIMMING is permitted at this time. Keep dogs away from water. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.  


Swim Beach Conditions [PDF] | Monitoring Program |

No Advisory Posted
Water Quality Notice - Lake Anza at Tilden

Cyanobacteria (blue-green algae) is present in lake, but no toxins have been detected recently. There are no advisories posted at the lake. As a precaution, keep dogs away from water. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

No SwimmingThe Swim Facility/Area is CLOSED for the 2022 swim season. 

What is covering Lake Anza? Click here to learn more about Azolla.

Swim Beach Conditions [PDF] | Monitoring Program |

Caution Advisory Posted
Water Quality Notice - Lake Chabot

Cyanobacteria (blue-green algae) is present at the lake and toxins have been detected recently. A Caution Advisory is posted around the lake. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

Swimming is never permitted at Lake Chabot.

Caution Advisory Posted
Water Quality Notice - Lake Temescal

Cyanobacteria (blue-green algae) is present in the lake, but all toxins detected recently have been below state advisory thresholds. There are no current cyanobacteria advisories. Keep dogs away from water. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

The Swim Facility/Area is OPEN.

Swim Beach Conditions [PDF] | Monitoring Program |

 

Danger Advisory Posted
Water Quality Notice - Horseshoe Lake / Niles Swim Beach

Cyanobacteria (blue-green algae) is present in lake and toxins have been detected recently. A Danger Advisory for cyanobacteria is posted at Horseshoe Lake and Niles Beach. No body contact with water is allowed and Keep dogs away from water. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

Swim Beach Conditions [PDF] | Monitoring Program |

 

Danger Advisory Posted
Water Quality Notice - Lago Los Osos at Quarry Lakes

Cyanobacteria (blue-green algae) is present and a Danger Advisory is posted at Lago Los Osos. Swimming is never allowed and water contact is not permitted at Lago Los Osos. Keep dogs away from the water. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

Swimming is never allowed and water contact is not permitted at Lago Los Osos.

No Advisory Posted
Water Quality Notice - Big Break Regional Shoreline

Cyanobacteria (blue-green algae) is present at the shoreline, but toxins detected recently have been below California advisory guidelines. There are no advisories posted at this time. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

No Advisory Posted
Water Quality Notice - Shadow Cliffs Lake

Shadow Cliffs swimming is CLOSED for the 2022 season due to low water levels. There are no cyanobacteria advisories at this time. See the Cyanobacteria (Blue-Green Algae) Information page for additional details.

Swim Beach Conditions [PDF] | Monitoring Program |

No Advisory Posted
Water Quality Notice - Contra Loma Reservoir

Cyanobacteria (blue-green algae) is present in the reservoir but all toxins detected recently have been below California state advisory thresholds. There are no current cyanobacteria advisoriesSee the Cyanobacteria (Blue-Green Algae) Information page for additional details.

Note: Cyanobacteria issues do NOT affect the Contra Loma Swim Lagoon water quality. 

Water Warnings Posted
Water Quality Notice - Keller Beach at Miller/Knox Regional Shoreline

Keller Beach is OPEN for swimming.


Swim Beach Conditions [PDF] | Monitoring Program |

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