The Louisiana Department of Health is warning residents to stay away from water where blue-green algae blooms are visible or suspected after a bloom was identified in Henderson Lake.

LDH announced Thursday that satellite imagery confirmed the presence of a cyanobacteria bloom in the lake. Although not all algae are dangerous, some types of cyanobacteria can produce toxins capable of making people and animals sick. Testing is necessary to determine whether a particular bloom contains those toxins.

The warning is not limited to Henderson Lake. LDH is urging people across Louisiana to recognize the signs of algal blooms and use caution in lakes, rivers and other waterways where they appear.

Blooms can change location and appearance quickly and may be blue, bright green, brown or red. Water may also develop foam or scum on the surface or have a strong odor similar to decaying plants. Blue-green algae grow particularly well in warm, calm and sunny water and are more common when water temperatures rise above 75 degrees.

LDH advises people who encounter a suspected bloom to stay out of the water and keep children and pets away. Swimming and wading should be avoided in affected areas, and the department also recommends avoiding boating or other recreational activities where an active bloom is present.

Pets should not be allowed to swim in or drink affected water. Anyone who accidentally comes into contact with the water should wash thoroughly with soap and clean water, and pets should also be washed after exposure.

Water from an affected area should not be used for drinking, cooking or preparing food.

Exposure to harmful algal toxins can cause symptoms including skin rashes, stomach cramps, coughing, nausea, diarrhea and vomiting. Higher levels of exposure can affect the liver and nervous system. Anyone who becomes ill after contact with water containing a suspected bloom should contact a healthcare provider.

LDH emphasizes that you cannot determine whether an algal bloom is toxic simply by looking at it. The safest approach is to avoid contact whenever a bloom is visible or suspected.

For health questions related to harmful algal blooms, residents can contact LDH’s Section of Environmental Epidemiology and Toxicology at 888-293-7020.

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