Edith on Water Features as Mosquito Control

by Edith Isidoro-Mills -- Our current weather may cause us to forget our summers can be long, hot and dry.  In such a hot, dry climate, incorporating water features such as ponds and fountains into your landscape is tempting.  Ponds and other water features can also breed mosquitoes which carry West Nile Virus unless they are properly designed and stocked with mosquito eating fish. Mosquitoes like to lay their eggs in still bodies of water; especially shallow (less than 6 inches) water, near over hanging plants, near aquatic plants, and in the partial submerged pots of containerized plants. Water features such as fountains and water falls that are continuously flowing will not harbor mosquito larvae unless they are turned off and water is allowed to sit still for any period of time.  The problem with flowing water features is many are also temporarily shut off and water is allowed to sit still for periods of time.  Such water features should be designed to drain completely when shut off. Usually ponds do not have constantly moving water so they are ideal mosquito breeding areas unless constructed deep enough, with little or no area less than 6 inches deep, and are lined with plastic or vinyl, and are stocked with a species of fish known to eat a significant quantity of mosquito larvae and eggs. A number of fish species will to eat mosquito larvae and eggs but koi are not among them unless starved.  Goldfish, killifish, and tadpoles do a better job of eating mosquitoes and are compatible with koi.  Unfortunately the goldfish, killifish and tadpoles that can be purchased at local pet shops are not winter hardy in our area and don’t do as good a job of controlling mosquitoes as the mosquito eating fish, Gambusia affinis.  Gambusia affinis, which reach a maximum size of 2 to 3 inches, are very aggressive and not compatible with other fish species. Before stocking your pond with fish it should be constructed or renovated to be at least 18 inches deep with very few aquatic plants and no overhanging plants on the edges.  If you live on the outskirts of town and occasionally have wildlife wandering through your property, a few submerged rocks may be necessary to provide cover for the fish when a raccoon visits. Mosquito eating fish can be obtained by contacting Churchill County Mosquito and Weed Abatement District at 423-2828. Once the pond is stocked conditions in the pond must be maintained such that there is no run off of pesticides that could kill the fish or fertilizer that could stimulate an algae bloom resulting in anaerobic conditions.  A build up of organic matter such as leaves and grass clippings in a pond could also cause the pond to become anaerobic thus killing the fish. To insure that mosquito control is being achieved in you water feature you should periodically dip a white cup in the water and check to see if there are any larvae.  If you find larvae, the pond may need more fish or it may need to be cleaned and restocked with fish. With proper construction and stocking of fish, a water feature in your yard can still be a joy in Churchill County.   Support local, independent news – contribute to The Fallon Post, your non-profit (501c3) online news source for all things Fallon. Never miss the local news -- read more on The Fallon Post home page.