State Water Board Reminds the Public to be Aware of Harmful Algal Blooms this Holiday Weekend

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SACRAMENTO — With many swimmers and boaters expected at the state’s lakes, streams and reservoirs this Labor Day weekend, the State Water Board is reminding the public to be mindful of harmful algal blooms (HABs) and to practice Healthy Water Habits, such as keeping pets away, if they see one.


Last week, the California State and Regional Water Boards conducted targeted sampling at some of the state’s most visited lakes and streams that have a history of HABs. This sampling was part of a collaborative effort with other state and local agencies to gather data and share it with the public. Those agencies included the California Department of Water Resources, Klamath Basin Monitoring Program, East Bay Regional Parks, Elem Indian Colony, Big Valley Band of Pomo Indians, and others.
The results of the targeted sampling for approximately 40 waterbodies are summarized in an interactive map. You can see which locations were sampled at each waterbody and recommended advisory levels. Recommended advisory levels are based on   cyanotoxin testing results and/or visual indicators confirming the presence of a HAB. Red and orange dots indicate waterbodies with limited water recreation (i.e., no swimming) due to elevated levels of cyanotoxins. Please be aware that HAB location, extent and toxicity can change quickly. The data in this map is subject to change as new information is received. The interactive map will be made available August 31, 2018 and can be viewed at:

Algae and cyanobacteria, the organisms that cause HABs, have existed for billions of years as essential components of freshwater ecosystems. But when certain conditions favor their growth – such as warm temperatures, stagnant water flows and excessive nutrient inputs – they can multiply very rapidly creating “blooms.” These blooms can produce toxins, and taste and odor compounds, that pose health risks to humans and animals. When blooms pose a risk, they are referred to as harmful algal blooms (HABs).

Cyanotoxins and algal toxins pose risks to the health and safety of people and pets, drinking water, and recreating in water bodies affected by blooms. They can also accumulate in fish and shellfish to levels posing threats to people and wildlife. Symptoms of HAB-related illness in people and animals are available from the Centers for Disease Control and Prevention (CDC), and by contacting the California Poison Control Center (1-800-222-1222).

This year marks the start of a multi-agency effort to track and record data on human and animal illnesses potentially related to exposure to HABs in California. The Water Boards, California Department of Fish and Wildlife, Office of Environmental Health Hazard Assessment, and California Department of Public Health, together with water managers, and county and state health officials have worked to investigate reported cases of health impacts potentially associated with freshwater blooms. Through August 27, 2018, the Water Board’s data collection system has received 6 reports of human illnesses and 12 reports of animal illness or death. The inter-agency illness workgroup will continue to monitor, evaluate, and report throughout the year, and will provide an update on the types and nature of problems seen at close of 2018.

Pets, especially dogs, are susceptible to HABs because they swallow more water while swimming and playing in the water. They are also less deterred by green, smelly water that may contain HABs. Animals can experience symptoms within minutes of exposure to the toxins. In the worst cases, animals have died. If your pet experiences these symptoms after exposure, contact your veterinarian immediately.

It is important to distinguish cyanobacteria/HABs from green algae and other non-toxic water plants that are not thought to pose potential hazards to health (Figure 2). HABs can be a variety of colors such as green, white, red or brown and may look like thick paint floating on the water. Cyanobacteria blooms have a grainy, sawdust-like appearance of individual colonies.

For help identifying a HAB, check out this visual guide fact sheet available on the CA HABs Portal here:


For more information, please visit: California Harmful Algal Blooms Portal at

Emerald contributor since March 2012


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