Harmful algal bloom confirmed at Discovery Bay; public urged to avoid water activities

DISCOVERY BAY – A “danger” advisory has been posted after testing of water samples collected from multiple locations of Discovery Bay in Contra Costa County confirmed the presence of harmful algal blooms, according to the State Water Resources Control Board and Central Valley Regional Water Quality Control Board. HABs can pose a threat to people and pets, and the advisory urges people to avoid swimming, boating and other activities and to keep pets out of the water until further notice.

Those visiting Discovery Bay should be aware of the elevated risk and are encouraged to follow the following guidance:

Danger

  • Stay out of the water until further notice, including watercraft.
  • Do not let pets and other animals drink or go into the water or go near the scum.
  • Stay away from scum and cloudy or discolored water.
  • Do not eat fish or shellfish from this water.
  • Do not use this water for drinking or cooking. Boiling or filtering will not make the water safe.

After residents filed multiple reports of a HAB and suspected related illnesses in Discovery Bay, the Water Boards collected water samples at seven sites on June 28 to confirm the presence of cyanobacteria and associated cyanotoxins, focusing on sites where reports were shared across town. While waterways on the west side of town have the highest advisory level posted, the east side also is posted with lower-level advisories recommending no swimming and keeping dogs out of the water. It is important to note that not all parts of the bay were sampled to inform localized conditions. Sites and associated advisories are included in the map below.

Cyanobacteria, a group of organisms that form HABs, can produce potent toxins. Health risks are associated with HABs, as they produce dermatoxins that can cause itching skin and rashes, as well as gastrointestinal distress, headaches, agitation and weakness, or abnormal breathing if HAB material is swallowed while swimming. Dogs and children are most susceptible to exposure because of their smaller body size, increased potential to swallow water while swimming and tendency to stay in the water longer. If you suspect exposure, wash your children and dog immediately.

The bloom in Discovery Bay appears suspended near the water’s surface. Bloom conditions can

change rapidly as the winds and waves move or concentrate the bloom into different regions of the bay. In some areas, the bloom may concentrate and form a film or scum on the water surface. The color of the water may also appear discolored as bright or dark green and brown.

The town of Discovery Bay, in coordination with the Contra Costa Environmental Health Department has posted advisory signs and messaging to notify residents and recreational users of the bloom. The Water Boards will provide regular updates to inform the community when postings are removed on the California HAB Reports Web Map.

The Water Boards recommend that people practice healthy water habits while enjoying the outdoors this summer at your local lake, river or stream:

  • Heed all instructions on posted advisories if present.
  • Avoid algae and scum in the water and on the shore.
  • Keep an eye on children and pets.
  • If you think a harmful algal bloom or toxic algal mats are present, do not let pets and other animals go into or drink the water or eat scum/algal mats on the shore.
  • Don’t drink the water or use it for cooking.
  • Wash yourself, your family and your pets with clean water after water play.
  • If you catch fish, throw away guts and clean fillets with tap water or bottled water before cooking.
  • Avoid eating shellfish if you think a harmful algal bloom is present.

Get medical treatment immediately if you think that you, your pet or livestock has gotten sick after going in the water. Be sure to alert the medical professional to the possible contact with cyanobacteria. Also, make sure to contact the local county public health department.

To report a bloom, do one of the following:

Fill out the Bloom Report form on the HABs Portal:

For more information about HABs, please visit:

California Harmful Algal Blooms Portal

Harmful Algal Blooms | Contra Costa Health (cchealth.org)