Blue-Green Algae

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Park scientists testing water sample.
 

Swimming NOTICE

Blue-green algae occur naturally in many lakes and rivers. While no toxic algae has been found in Lake Mead or Lake Mohave in 2019, they have been found in parts of the lakes in past years. Algae are more abundant in summer and may appear as green or yellow streaks or scum on the surface of the water or as green globs or streaks floating below the surface. Algae may produce toxins.

As a precaution, recreational visitors should follow a few safety tips where algae are present:

  • Do not swim, dive or contact water in areas with algae.
  • Do not drink untreated lake water. (Boiling, filtration and chlorine tablets will NOT remove the toxin.)
  • Keep pets and children out of areas with algae.
  • Clean fish well, and discard guts.
 
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Close-up of algae
 

Allergic Reactions

The algae and the water around it can cause allergic reactions and illness in pets and people. Symptoms include eye and skin irritation, rashes and abdominal pain, cramps and diarrhea. Contact your doctor or veterinarian if you or your pets have symptoms or sudden illness.

According to the Southern Nevada Water Authority, the algae do not pose a threat to Southern Nevada's drinking water. The SNWA's treatment plants utilize both ozone and chlorine, which represent the two most effective water treatment processes, and it will prevent algae from entering the community's water system.

While the likelihood of people being affected by contact with blue-green algae is very low, federal, state, and local agencies in Southern Nevada will continue to proactively monitor algae composition levels in lakes Mead and Mohave. Most areas of the lakes do not have accumulations of algae. Visitors and their pets can continue to enjoy the water where algae are not present.

To report algal blooms or illness, call 702-293-8998.

To report a medical emergency, call 702-293-8932.

 
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Measuring the clarity of the water.
 

Questions & Answers

Blue-green algae, also called cyanobacteria, occurs naturally in many lakes and rivers around the world and have been found in parts of lakes Mead and Mohave in the past. Blue-green algae are actually not plants but rather a type of bacteria which photosynthesizes like plants. In warm, nutrient-rich water, blue-green algae can grow and potentially cover large areas of the surface.
Blue-green algae can vary in color and appearance and may look like pea soup or spilled green paint on the surface of the water, green or yellow streaks or scum on the surface of the water or green globs or streaks floating below the surface.
Some blue-green algae can produce toxins harmful to people and pets. At least one-third of lakes in the United States that are larger than 10 acres have these toxin producing algae, and this trend is increasing worldwide. Not all algae produce these toxins, and it is impossible to tell if the algae are toxic or not just by looking at the concentration. Therefore, one should avoid contact with any blue-green algae to prevent contact with any potential toxin.
The algae and the water around it can cause allergic reactions and illness in pets and in some people. In people, skin contact with the algae can cause eye and skin irritation and rashes. Ingesting algae can cause abdominal pain, cramps and diarrhea. In pets, symptoms of ingesting algae can include weakness, loss of appetite, drooling, vomiting and diarrhea, abdominal tenderness and dark urine. As always, don’t drink untreated water straight from the lake.
Pets are more likely than humans to be exposed because they do not naturally avoid entering and ingesting the algae. Young children are also at higher risk due to their smaller size.
Contact your doctor or veterinarian if you, your children or your pets have symptoms or sudden illness after being in water with blue-green algae.
 
For more information, visit the CDC website.
 

Last updated: August 29, 2019

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