PORTLAND, Ore. (KOIN) – Oregon State University is warning people against releasing non-native fish into waterways this summer as a way to manage the increased number of mosquitoes. 

Researchers say non-native fish, such as the guppy and the western mosquitofish, are sometimes released into public and private ponds and wetlands to try to control the pesky insect. These two common non-native fish eat mosquito larvae. 

However, Sam Chan and Dana Sanchez, from OSU’s Department of Fisheries, say these do-it-yourself solutions aren’t effective for mosquito control and aren’t good for the environment. 

It’s against the law in Oregon to release non-native fish into any public waterway and a permit is required for private land. Placing these fish in small backyard ponds and other water features might seem safe, but can cause problems if a flood allows them to escape. 

“Those wanting to or who have made these releases may not know that there are more effective long-term solutions or realize that Gambusia (western mosquitofish) will consume much more than mosquito larvae, including native fish, amphibians, invertebrate insects and zooplankton,” Chan said. “In western Oregon, many of the native fish, amphibians and aquatic invertebrates such as dragonflies also consume mosquito larvae.” 

Chan said he’s concerned that released western mosquitofish and guppies also consume zooplankton, which consume algae. If there’s not enough zooplankton in bodies of water, harmful algal blooms can get out of control. 

Researchers believe the record mosquito year is likely the result of a wet spring. They think the sub-freezing temperatures in April likely destroyed many frog eggs, allowing fewer of these mosquito predators to hatch than in other years. 

“Field sampling this year has revealed that quite a few previously active and even abundant frog sites had low to no reproduction this year,” Sanchez said. 

To help control the mosquito population, the Oregon Department of Fish and Wildlife recommends people minimize standing water around their homes. This includes eliminating water-filled containers such as buckets and old tires, cleaning roof gutters and managing water troughs and bird baths. 

Sanchez said a targeted biological control for mosquito larvae is Bacillus thuringiensis israelensis, better known as Bti. This is a bacterium that occurs naturally in soils and it’s widely available at retail locations. It’s safe around mammals, birds, fish and amphibians. 

Acoustic sonic devices are another effective tool for controlling mosquito larvae.