Mantua Reservoir file

A sign posted in August at the bathroom near the beach at Mantua Reservoir warns of harmful algae in the water.

Health officials have closed the North Beach at Mantua Reservoir due to a harmful algae bloom.

The rest of the reservoir isn’t closed but has been under a “warning advisory” since the latter half of last month. on Monday the Bear River Health Department upgraded specifically the North Beach to a “danger advisory.”

North Beach is closed and people are warned to stay out of the water. The advisory for the rest of the reservoir warns people not to swim or water ski, not to drink the water and to keep pets and livestock away from the water. Fishing is still allowed outside of the North Beach area, but fishermen are advised to thoroughly clean fish and discard the guts.

Elsewhere in the state, the Utah Department of Environmental Quality issued a warning advisory for Utah Lake on Monday. As with Mantua Reservoir, people are advised not to swim in, water ski in or drink water from the lake. Officials are expected to reevaluate the lake at the end of the month.

Exposure, especially by ingestion, to water from a lake or reservoir undergoing an algae bloom can be harmful because certain types of algae — including cyanobacteria, which has been found in high concentrations in multiple samples from Mantua and Utah Lake this summer — produce toxins.

If you believe a person or animal has been exposed to a harmful algal bloom, the DEQ recommends calling the Utah Poison Control Center at (800)222-1222.

Algae multiplies rapidly when a body of water is high in nutrients and when high sunlight accelerates growth. Excess nutrients like nitrogen and phosphorus get into bodies of water when runoff contains fertilizer from lawns and fields.

For more information and updates, check deq.utah.gov/health-advisory-panel/mantua-reservoir.

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