BREAKING: DANGER levels of cyanotoxin found in Discovery Bay

This is a message from the California Regional Water Quality Control Board, Central Valley. 6/10/20

Good Afternoon,

The Water Boards received a report of significant cyanobacteria harmful algal bloom (HAB) occurring in Discovery Bay, including multiple locations at the DANGER level (highest threshold). This afternoon (6/10/2020) State Water Board’s HAB Hotline received lab results of the June 4th water samples collected from Discovery Bay by Central Valley Regional Water Board staff – results are summarized in the table below.

Incident Details:

• Extensive cyanobacteria HAB throughout the bay with elevated cyanotoxins in the bloom material that accumulates near slow moving areas (e.g. coves, docks).

• Multiple cyanobacteria genus (Microcystis and Dolichospermum) detected at all locations sampled.

• Microcystins exceeding recommended CCHAB trigger levels for posting planktonic advisory signs, up to 13 times higher than the Danger level (highest threshold).

• Numerous residents of Discovery Bay have reported HAB observations, including in areas not sampled on June 4th.

Microcystins (ug/L)
Recommended Signage
Sample #
Site Water Sample Scum 

Windward Bay

Clipper Bay

Discovery Bay Yacht Club

Next Steps:

• Post recommended Danger signs at public access points at or near sampling locations. If durable signs (not paper) are needed, please request assistance by replying to this email. The HAB Hotline may be able to provide durable signs (PVC plastic).

• Consider posting Caution sign at additional areas if visual indicators (discolored water, mats/scums, paint-like appearance) observed.

• Many of the residents of Discovery Bay that have contacted the HAB Hotline are seeking additional information regarding management practices to prevent blooms in the community. We recommend the community officials distribute informational leaflets to residents, the Frequently Asked Questions fact sheet on the HABs Portal could be utilized for outreach.

• Request Division of Drinking Water and Dept. Of Water Resources staff coordinate with entities who have downstream drinking water intakes.

• State Water Board will request public notification via the Water Board public information officer and will also post the recommended advisories to the Water Boards FHABs web map.

• Continue coordination with State Water Board (via email) and Central Valley Regional Water Board (Matt Krause as new HAB coordinator;

• Report any potentially HAB-related illness reports by submitting an online bloom report (or email to

• HAB-related illness workgroup will notify nearby veterinary and medical hospitals.

Thank you in advance for your assistance.


Marisa Van Dyke
HAB Hotline
State Water Resources Control Board

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