Nevada County to Distribute Mosquito Fish for Disease Prevention

NEVADA CITY — The Nevada County Environmental Health Department has announced a series of mosquito fish giveaways to help reduce mosquito populations and lower the risk of mosquito-borne diseases, especially West Nile Virus. The giveaways are scheduled for five Wednesdays from May 7 to July 9, 2025, at the Nevada County Government Center in Nevada City.

Mosquito fish, scientifically known as Gambusia affinis, are small fish that feed on mosquito larvae. They serve as an effective biological control method for mosquitoes in standing water. Amy Irani, Director of Environmental Health, highlighted their role: “Mosquito fish are named as such because they are known to consume quite a bit of mosquito larvae in ponds or other standing bodies of water.” By targeting larvae, these fish help decrease the adult mosquito population and reduce the potential for disease transmission.

Distribution Schedule

Residents can pick up mosquito fish on the following Wednesdays:

May 7, 2025

May 21, 2025

June 4, 2025

June 18, 2025

July 9, 2025

Each giveaway will occur from 10:00 AM to 12:00 PM in the parking lot of the Nevada County Government Center, located at 950 Maidu Avenue, Nevada City, California. The events will follow a drive-thru format, with participants requested to remain in their vehicles. Containers will be provided for safe transportation, and the fish must be placed in a designated water source—such as a pond, watering trough, birdbath, or unused swimming pool—within two hours of receipt.

Environmental Considerations

Mosquito fish are non-native to the region and can become invasive if introduced into natural waterways. They should only be used in closed or stagnant water bodies without outlets to local creeks or streams. Releasing them into natural ecosystems may harm native species and biodiversity. If a pond already contains larger fish, mosquito fish are unnecessary, as the larger fish will consume mosquito larvae and may also prey on the mosquito fish.

Alternatives for Temporary Water Sources

For temporary or seasonal water sources, such as ditches or drainages, which cannot be drained, bacterial larvicide products like BTI (Bacillus thuringiensis israelensis) are recommended. BTI specifically targets mosquito larvae without affecting other organisms and is safe for humans, pets, and wildlife when used as directed. These products can be found at local hardware, garden, or pond supply stores. The Nevada County Environmental Health Department also provides on-site consultations and treatment services. Residents can reach the Vector Control Program at (530) 265-1500 for assistance or additional information on vector management.

Participation Instructions

To obtain mosquito fish, follow these steps:

Arrive at the Nevada County Government Center parking lot between 10:00 AM and 12:00 PM on one of the specified dates.

Follow directional signage to the drive-thru pick-up area.

Stay in your vehicle; department staff will provide the fish and instructions.

For more resources on mosquito fish and vector control, visit the Nevada County Environmental Health Department’s website.