California officials urge caution after harmful algae bloom found in lake

California health officials are warning residents and visitors to act with caution after harmful algae was found in Madera County's Hensley Lake. 

"Central Valley Water Board staff observed high amounts of harmful algae and cyanobacteria (sometimes called blue-green algae) at Hensley Lake," the Madera County Department of Public Health wrote on Facebook last weekend. "HABs can make toxins that can be harmful or fatal to people, pets, and livestock."

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"Harmful algal blooms (HABs or blue-green algae) are an annual event in the Central Valley.," the department said in a post on its website. "HABs can create toxins that are harmful to people and animals. Madera County lakes, such as Hensley & Eastman are monitored by the California Waterboard for HABs, but this is not true for all bodies of water within the county (depends on size, ownership & jurisdiction)."

Those who frequent these lakes are instructed to follow warning signs, which are now placed around Hensley Lake, according to KFSN.

While swimmers, fishermen and others can still enter the water, the U.S. Army Corps. of Engineers – which posted the signage – is asking people to make smart choices. 

"If you are going to get in the water, make sure you’re not getting in an area where you can visibly see the scum. It's a bright green paint-like color in the water and you wanna avoid those areas," Doug Plitt, the Operations Project Manager with the U.S. Army Corps. of Engineers at Hidden Dam, Hensley Lake, told Fox 26 on Monday.

Plitt told the station that blue-green algae is common in the period between summer and early fall and that it accumulates in coves.

According to the California Water Quality Monitoring Council, the cyanobacteria and HABs can occur in both freshwater and estuarine waterbodies. 

Increased nutrients like nitrogen and phosphorus promote cyanobacterial growth and additional aspects like stagnant water, increased intensity and duration of sunlight, sustained high temperatures and low flows create "ideal conditions" for the blooms.

"Current research suggests that the rising temperatures and changing precipitation patterns caused by climate change are a catalyst for their growth," the agency noted on its website.

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The algae and cyanobacteria, often seen as a "scum" on the water's surface or floating below, can produce harmful compounds that pose threats to both human and animal health.

"Cyanotoxins and algal toxins pose risks to the health and safety of people and pets, drinking water, and recreating in water bodies affected by blooms. They can also accumulate in fish and shellfish to levels posing threats to people and wildlife," the Water Boards wrote. "Pets, especially dogs, are susceptible to HABs because they swallow more water while swimming and playing in the water, and are also less deterred by green, smelly water that may contain HABs."

"If you get it on your skin it could cause irritation to the skin rashes," Plitt told Fox 26, "If you ingested the water that had cyanotoxins in it you would maybe feel nausea, headache, dry mouth, vomiting and you would want to contact a doctor right away."

Signs of potential exposure may occur within 48 hours and could include sore throat or congestion, coughing, or difficulty breathing, red or itchy skin, blisters or hives, earache or irritated eyes, diarrhea or vomiting, agitation, headache and abdominal pain.

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Investigators are looking into whether a toxic algae bloom may have contributed to the recent deaths of a Northern California family and their dog on a remote hiking trail in the Sierra National Forest.

The Central Valley regional water quality control board will continue routine water monitoring, KFSN said, with a period of two weeks of bloom-free water necessary to lift the advisory.