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Southern Nevada Water Authority

Algae in Lake Mead


Algae in Lake Mead in 2001.

Algae is common in most bodies of both fresh and salt water. The widespread bloom of the green algae species (Pyramichlamys) seen in bays and coves at Lake Mead in 2001 was a highly unusual event caused by a unique combination of hydrologic factors.

This particular species of green algae is most likely to bloom when a sequence of warm and cold temperature changes occurs over a short period of time and when there is phosphorus and nitrogen available on the lake's surface.

Although it reduces the clarity of the water, green algae poses no threat to Southern Nevada's water quality. The algae bloom occurs only near the surface of the lake, approximately 100 feet higher than the intake pipes that draw drinking water.

Additionally, this species of algae is not toxic and could be removed from the water during the treatment process. Algae growing in Boulder Basin or any other body of water is a normal event, and is in fact beneficial to aquatic life. Additionally, the algae is not considered a recreational health hazard.

Sources of phosphorus in the lake include wildlife, treated wastewater and urban runoff. While the valley's wastewater treatment agencies are voluntarily reducing the amount of phosphorus reaching the Las Vegas Wash, residents can further reduce the amount of phosphorus available for algal growth by correcting lawn care practices.

The combination of over fertilizing and subsequently over watering lawns results in concentrated phosphorus flows entering the lake through urban runoff. The SNWA recommends residents apply the proper amount of fertilizer as indicated on the package and follow the SNWA's lawn watering guides.


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