Recent testing yielded positive results for small amounts of toxic algae in Deadman Creek and visual
observations made at Hummingbird and Odell Lakes in the 20 Lakes Basin may indicate toxic algae is
also present in these two lakes. Toxic algae may exist in other sites on the forest.
Toxins are concentrated within the algal mats themselves and released episodically into the water
when the algae dies or is disturbed.
For your safety, do not enter the water or drink in these areas. Filtering and/or boiling the water is not
effective against this type of algae.
Prevent pets from drinking the water and eating or touching algae in the water and dried on the shore.
In particular, prevent dogs from eating dried algal mats on shore.
Please report any large algal blooms and/or algae that is particularly bright, bubbly, strange-looking, or
appears like a haze in the water.
Do not disturb algal mats in any way. Wading or swimming can cause toxins to be released into the
If you suspect a site has toxic algae, do not enter the water and do not drink water from the area. While
some sites are signed based on testing results, it’s likely that algae exists in other parts of the forest.
Don’t rely on signage alone.
According to the California Water Quality Monitoring Council, the following signs and symptoms may
occur within 48 hours of exposure to a waterbody with a suspected or confirmed algal bloom:
• sore throat or congestion;
• coughing, wheezing, or difficulty breathing;
• red, or itchy skin, or a rash;
• skin blisters or hives;
• earache or irritated eyes;
• diarrhea or vomiting;
• headache; and/or,
• abdominal pain.
If people show symptoms of cyanotoxin and/or cyanobacteria exposure after contact with water, or with
scums or mats of algae, they should receive immediate medical attention. Additional resources are
available from the Centers for Disease Control and Prevention (CDC), and by contacting the California
Poison Control Center (1-800-222-1222). See the HAB-related Illness Tracking webpage for
information on previously reported human illnesses related to HABs in California.