State Water Board urges caution around harmful algal blooms ahead of Memorial Day weekend

SACRAMENTO – As the mercury climbs and Californians head outdoors for the unofficial start of summer, the State Water Resources Control Board is urging the public to stay alert for harmful algal blooms (HABs) in lakes, rivers and reservoirs across the state.

Californians value access to the state’s lakes, rivers and reservoirs for outdoor recreation and enjoyment. With Memorial Day weekend approaching, awareness of harmful algal blooms can help people safely enjoy these important natural resources.

HABs are caused by certain types of cyanobacteria that can produce toxins harmful to people and animals. While some blooms are easy to spot, others are less obvious — and no matter how much a person may know about science, it’s not possible to determine whether a bloom is toxic just by looking at it.

Before heading out, check current conditions on California’s HABs map and look for posted advisories at your destination.

The board recommends avoiding water that has:

• Bright green, blue-green, or reddish discoloration.
• Paint-like scum or streaks on the surface.
• Thick mats or clumps, especially along the shoreline.
• Murky or cloudy conditions.

When in doubt, stay out — and keep pets away.

Already this month, three danger advisories have been issued for algal blooms in Lago Los Osos in Alameda County, Eastman Lake in Madera County and Harveston Lake in Riverside County. Warmer conditions can exacerbate the growth of HABs, so incidents are expected to increase over the summer.

“People often have just a few seconds to decide whether the water is safe,” said Marisa Van Dyke, a senior environmental scientist with the State Water Board’s Freshwater Harmful Algal Bloom Program. “If the water looks unusual — discolored, cloudy, or covered in scum — the safest choice is to stay out.”

HABs can appear in different forms. Some float in the water and create green or blue-green streaks or a paint-like sheen. Others form thick mats along the bottom or shoreline.

These shoreline mats can pose a particular risk to dogs, which may ingest algae while drinking or grooming. In some cases, exposure can lead to serious illness within minutes to hours.

Dogs don’t just swim, they drink the water and can ingest algae along the shoreline. Pet owners are urged to be especially cautious and keep dogs away from discolored water or algal mats. California’s HABs response relies heavily on reports from the public. When a potential bloom is reported, staff coordinate with local agencies to assess conditions, collect samples and determine whether advisories or warnings are needed.

“Public awareness plays a critical role,” said Van Dyke. “If something doesn’t look right, reporting it can help protect others.”

For more information, to view current conditions, or to report a bloom, the public should visit the Water Quality Monitoring Council’s website.

This week’s story on the board’s new digital publication, Ebb and Flow, features photos, tips and guidance on keeping pets and children safe from harmful algal blooms.

The State Water Board’s mission is to preserve, enhance and restore the quality of California’s water resources and drinking water for the protection of the environment, public health, and all beneficial uses, and to ensure proper resource allocation and efficient use for the benefit of present and future generations.