While arriving at a lake or reservoir in Nevada to do some fishing, swimming, boating, water skiing, or playing with the dog in the water, you may encounter one of these posted signs:
Placement of signs indicates that water conditions have deteriorated as a result of a harmful algae bloom. These blooms can pose serious health risks to people and animals (pets) since they are comprised of toxin producing bluegreen algae. The strength of the toxin determines whether the bloom warrants a “Warning” or “Danger” classification. Since there is no way to determine the presence or toxicity by simply looking at the water, algae must be examined under a microscope and toxicity must be tested by laboratory analysis.
However, most open-water algae are beneficial and become part of a healthy lake system. They are important in creating dissolved oxygen for fish to survive while also being the foundation of the food chain. Some fish filter and eat algae directly from the water, but more importantly, small planktonic animals (related to shrimp and crabs) that consume algae become food for young or filter feeding fishes. One thing to note, levels of toxins in fish from harmful algae blooms found in Nevada are usually low enough that the fish can still be eaten. If you are at a posted water body or are concerned about water conditions, wash your fish with clean water and only eat the filets, disposing of the skin and guts.
Although cyanobacteria do not always produce toxins, algal blooms can develop when nutrients (similar to fertilizers on a lawn) are high, temperatures are warm, and the water becomes stagnant. Depending on lake conditions, an algae bloom can develop rapidly. Bluegreen algae often concentrate near or at the water surface creating scum-like blooms that are greenish (in many cases), but can be light blueish, whitish, brownish, or reddish (or a combination) in color.
If you happen to be at a lake or reservoir having one of the posted harmful algae bloom signs, it is best to follow the guidelines. However, because blooms can develop quickly, you may find yourself at a water body that has yet to be tested. In this case, use common sense and be aware that the bloom can be toxic. “If in doubt, stay out.” To review further precautions, possible symptoms if you should become exposed, and phone numbers for reporting blooms or illnesses from a bloom, please check out these resources: