Monsoon season has arrived, perhaps finally providing some relief from June’s extreme heat. But with the more humid weather also comes standing water and mosquitos, a combination that can also bring transmitters of diseases such as the West Nile and Zika viruses.

Salt River Project has been doing its part since 2004 to help combat the spread of mosquito-borne diseases by stocking its 131 miles of canals in the Valley with Gambusia affinis fish – about 200,000 each year have been eating mosquito and thriving on larvae during the 13-year-old program.

SRP, which also employs white amur fish in its canals to reduce the need for herbicides to control aquatic weeds, this week will be wrapping up its annual stocking for the year when bags of tiny mosquito fish will be released into canals and laterals. The expectation is that these fish will eventually make their way into culverts and ditches where standing water is more likely to occur.

Brian Moorhead, a senior scientist/engineer in SRP’s Groundwater division who heads up the stocking program, said SRP’s canals are not conducive to mosquito reproduction because the water is constantly moving.

“These fish are only 1 to 2 inches long, and they can move into our smaller laterals and ditches to help curb the mosquito populations there,” said Moorhead. “Much of the infrastructure that delivers SRP irrigation water connects to residential shareholders’ privately owned irrigation facilities such as ditches, pipes and standboxes, which can have pools of water that last for several days. These fish can then use the pipelines as conduits to assist in removing mosquito larvae.”

The small fish are purchased from fish farms in North Carolina and arrive via air freight in batches of approximately 15,000 per shipment. Upon arrival, the fish are distributed among several SRP canal sites from which they can make their way into the lateral system.

SRP is the largest raw water supplier in the greater Phoenix metropolitan area, delivering about 800,000 acre-feet annually to agricultural, urban and municipal water users.