The U.S. housing market might be going to the dogs, but the swimming pools are going to the mosquitoes. As foreclosures force homeowners out, mosquitoes that could be carrying the West Nile virus are moving in, taking advantage of abandoned swimming pools, hot tubs and ornamental ponds.

A study in Emerging Infectious Diseases reports that last summer in Kern County, California, cases of human West Nile virus jumped 276 percent following a 300 percent increase in home mortgage delinquencies.Aerial photos [pdf] showed that 17 percent of visible pools were green with algae blooms and probably breeding mosquitoes.The surge happened after a particularly dry season that should have suppressed mosquito numbers.But instead, populations of the urban strain (Culex pipiens quinquefasciatusi) increased rapidly and earlier than expected.This summer, the researchers noticed that a rural strain (Culex tarsalis), which is more virulent, has begun breeding in abandoned pools as well.

Making matters worse, the law requires outdoor swimming pools to be surrounded by a secure fence at least 2 meters high.What was supposed to keep out little kids is now keeping out mosquito-control workers trying to identify and treat neglected pools.

Kern County

isn’t alone.This year, Nassau County, New York—where a quarter of homes have swimming pools—reported a spike in West Nile virus that prompted officials to order aerial pesticide spraying.Pool-friendly states like California, Florida, and Arizona have resorted to seeding stagnant pools with mosquito-eating minnows, nicknamed (aptly) the foreclosure fish.

Image: flickr/ nikpawlak