Low concentrations of harmful cyanobacteria, or blue-green algae, have been detected in Lake Mendocino near Ukiah, the U.S. Army Corps of Engineers said.
According to the Army Corps, the current bacteria levels do not pose a significant health risk to people or pets, despite signs dotting the shorelines asking that people and pets stay away from the algae.
The signs warn that harmful algae may be present in the water and that people can swim in the water, but should avoid contact with algae and scum, including on the lake shore.
The Army Corps also asks that pets and other animals should avoid swimming in or drinking the water. Pets also need to stay away from any algae scum on the shore.
The reservoir water should not be used for drinking and no shellfish from the reservoir should be eaten.
The signs also recommend that any fish caught in the lake should have the guts removed and the fillets should be cleaned with bottled or tap water before cooking.
The Army Corps asks that reservoir visitors see a medical doctor if they experience skin irritation, nausea, vomiting or diarrhea after coming into contact with the water. Pets that experience the same symptoms should be taken to a veterinarian.
Warning comes weeks after tests showed no bacteria was found at the reservoir
The Thursday announcement comes more than six weeks after the Army Corps said the reservoir was free of cyanobacteria after a visitor’s post on social media said their dog had died due to bacteria intake.
Toxin-producing cyanobacteria is more likely to occur in late summer, said Mike Thomas, North Coast Regional Water Quality Control Board regional monitoring coordinator. Visible algae blooms floating above the surface of the water can be caused by rapid population growth of cyanobacteria.
“Testing of the water sample showed a small amount of cyanobacteria, which can produce toxins, but the levels were very low,” the Army Corps said. “We also found a very small amount of one type of toxin, anatoxin, but it was at the lowest level our testing could detect.”
Many factors result in the rapid growth of cyanobacteria, Thomas said, including heat, drought and agricultural runoff.
Cyanobacteria usually manifests in lakes and reservoirs as planktonic algae, which floats to the top of water and can cause the water to turn green, he said.
“In the planktonic bloom, toxins may be diffused in the water column,” Thomas said, so clear water may still contain toxins. Testing is important in lakes and reservoirs as it is often the only way the public can know if toxins are present.
Alerts also issued for East Fork of Russian and Navarro rivers
Cyanobacteria algal mats, or benthic algae, have been found in two Mendocino County rivers popular with recreation, according to the state’s Water Quality Monitoring Council.
Algal mats were discovered on Aug. 20 in the East Fork of the Russian River near Elledge Ranch Road, approximately 1.5 miles east of Lake Mendocino. The river feeds into Lake Mendocino.
An alert was also issued Monday for a part of the Navarro River that runs through Hendy Woods State Park in the unincorporated community of Philo.
How to stay safe and reduce risk of illness while recreating rivers and lakes
If a body of water tests positive for HABs, state agency representatives will place public notices onsite. Check for warning signs and act appropriately based on what the sign advises.
People swimming in rivers or free-flowing creeks should stay away from floating mats of algae. As noted above, algae itself is natural. However, if swimmers notice mats, especially mats that look oily or slick, exercise extra caution. If people see dead fish or animals nearby, steer clear.
In general, a good rule is to rinse off after exiting waterways as soon as possible and try not to swallow any water from the creek or river.
When playing with dogs, specifically throwing balls or objects, keep to the area where water is visibly moving, not in pockets or swimming holes. Bring bottled water and a travel dish and encourage pets to drink on shore, discouraging dogs from drinking from the river.
In lakes and reservoirs, there may be no algae to alert swimmers and pet owners. If the water is warm, assume that cyanobacteria could be present. People and pets should not drink lake water and bring bottled water to enjoy instead.
Dogs could become sickened by licking their fur after swimming in water impacted by algae. Bring a gallon jug of water and after the last swim, empty the jug over dogs from head to tail, then rub them with a towel to clean off lake water. All this should go a long way to preventing heartache if pets — or people — become ill.
The public can report suspected or confirmed algal blooms and any related human or animal illnesses to the California Water Quality Monitoring Council here.
The council, in partnership with the Army Corps, monitors water conditions daily here, for bodies of water frequently used for recreation or other public uses.
An interactive map of testing results across the state is also available here.
Test results and tips on staying safe when recreating in areas impacted by algal blooms can be found at mywaterquality.ca.gov.
This story originally appeared in The Mendocino Voice.