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High Temperatures and Summer Rain Increase West Nile Virus

LAKEPORT, Calif. – The recent high temperatures and unusual summer rain have created an opportunity for mosquitoes and West Nile virus to thrive.

This year, five samples of mosquitoes collected in Lake County tested positive for West Nile virus (WNV).  The WNV-positive mosquito samples were collected near Clearlake Oaks, Lower Lake, Middletown, and Upper Lake (2); all were Culex tarsalis (western encephalitis mosquito).

“Both mosquito and West Nile virus activity increase when the overnight temperatures are 60°F or warmer,” said Jamesina Scott, Ph.D., District Manager and Research Director of the Lake County Vector Control District.  “With so many other things happening, like the fires and COVID-19, many people don’t think about mosquito-borne illnesses.  Mosquitoes cannot transmit coronavirus, but they transmit West Nile virus.  The best way to protect yourself is avoid mosquito bites.  If you plan to be outside when mosquitoes are active, apply an effective repellent that contains Picaridin, IR3535, Oil of Lemon Eucalyptus, or DEET.”

Mosquitoes develop in water, so you can protect yourself and your family from mosquito bites and West Nile virus by dumping out standing water.  Now is a great time to take a walk around your yard and look for places that might hold water like buckets, toys, and boats and dump out any water you find.  If you have water that can’t be drained, like a pond, livestock watering trough, water feature, or an out-of-service (green) swimming pool, then contact the District and we can provide free mosquito-eating fish to prevent mosquitoes from growing there.

Lake County Vector Control District continues to provide mosquito control services to our community.  If residents need help with a mosquito problem, please call the District 7:30 AM -4:00 PM Monday through Friday, or request service online anytime at  

The District encourages residents to reduce their risk of contracting West Nile virus and other mosquito-borne diseases by:

• Dumping or draining standing water to prevent mosquitoes.  Mosquitoes need water to complete their life cycle.
• Defending yourself.  Use repellents containing DEET, Picaridin, IR3535, or Oil of Lemon Eucalyptus.  Follow the label directions.
• Avoiding the outdoors when mosquitoes are present, typically dawn and dusk

So far this year, West Nile virus activity has been detected in five mosquito sample in Lake County.  Statewide, 28 California counties have detected WNV this year, mainly in mosquitoes. As of August 14, 2020, 18 human cases of West Nile virus illness have been reported in California residents this year.

Residents with questions or who would like help with a mosquito problem, including reporting a neglected pool or spa, or have an in-ground yellowjacket nest on their property that they want treated, should contact the Lake County Vector Control District at (707) 263-4770 or visit their website at
For more information about West Nile virus, visit  Information about mosquito repellents can be found on the US Centers for Disease Control and Prevention website at

Water Faucet
Urgent Health Advisory

Effective immediately, people on private water systems whose tap water comes from their own private intake into the lake, in the Oaks Arm and Lower Arm of Clear Lake should not drink the water.

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