Bureau of Reclamation
The Trinity River.
Officials are urging people recreating on the Trinity River to exercise caution after a dog's recent death led to the discovery of a harmful algal bloom on the river.
According to the State Water Resources Control Board, staff responded to a report of a potential toxic-algae related dog death and collected samples July 7 at the Hlel-Din river access site and confirmed that "toxic algal mats" of Cyanobacteria, commonly known as blue-green algae, are growing on the bottom of the river.
"Because children and dogs are most susceptible to serious health impacts from HABs, it is recommended that they avoid touching any suspicious-looking algal material found in the water or along riverbanks," the agency advised in a press release. "Trinity County has posted 'Toxic Algae Alert' and 'Caution' signage at recreational areas along Trinity River, including swimming access areas downstream of the bloom. Boaters and recreational users are urged to be alert when recreating in the water."
For more information, view the full press release copied below:
Harmful Algal Bloom in Trinity River;
Caution Urged for all Water Users
Toxic algae pose serious threat to children, pets
July 20, 2021 Contact: Edward Ortiz
Sacramento – The State Water Resources Control Board and Trinity County advise caution for anyone who boats, fishes, or swims in the Trinity River (Trinity County) as a Cyanobacteria Harmful Algal Bloom (HAB) was recently discovered in the river. Because children and dogs are most susceptible to serious health impacts from HABs, it is recommended that they avoid touching any suspicious-looking algal material found in the water or along riverbanks.
The Water Boards and Trinity County staff recently responded to a report of a potential toxic algae-related dog death. They collected samples on July 7, 2021 at the Hlel-Din river access site for testing and confirmed that toxic algal mats are growing on the bottom of the river. Algal material from these mats may detach and become stranded on banks.
Toxic algae appear to impact the main stem of the Trinity River, extending downstream from the confluence of the South Fork Trinity River. Trinity County has posted “Toxic Algae Alert” and “Caution” signage at recreational areas along Trinity River, including swimming access areas downstream of the bloom. Boaters and recreational users are urged to be alert when recreating in the water. Trinity County and the Water Boards will provide regular updates to inform the community when postings are removed on the California HAB Reports Web Map.
About Harmful Algal Blooms (HABs)
While harmful algal blooms are caused by algal or cyanobacteria that grow floating in the water, some algae or cyanobacteria grow attached to the bottom surface of waterways and can form algal mats. If you see algal mats the recommendation is for children, dogs, and adults to not touch or inadvertently ingest any algal mat material in the water or found stranded on the riverbanks. In addition, dogs should not drink water directly from the rivers. These recommendations are based in research on the potential health risks posed by the toxins that can be produced by algal organisms, commonly cyanobacteria, that can form algal mats. Toxic algal mats can be found either attached to the bottom, floating in the water, or stranded on the riverbank. The appearance of algal mats ranges from bright to dull-green, orange, brown, and maroon material. In summary, when in doubt, avoid touching algal mats.
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 portal
Call the HABs hotline: 1-844-729-6466 (toll free)
Contact Trinity County Environmental Health at 530-623-1459
For more information about HABs, please visit:
California Harmful Algal Blooms Portal
Trinity County webpage