As foreclosed houses lay dormant and owners of occupied homes pinch pennies, a growing number of swimming pools are turning a “greenish-brown hue,” reports the Chicago Tribune today. That color signals a haven for moisture-loving and disease-carrying mosquitoes.

“If the water is pretty stinky, [mosquitoes] will find it, and they will lay their eggs on it,” Mike Szyska, director of the Northwest Mosquito Abatement District in Illinois, told the Tribune. He noted that one mosquito can lay as many as 250 eggs in a batch.

Chlorination and regular pumping deter mosquitoes, but as swimming pool owners run low on funds for this upkeep—or are forced to abandon their homes and pools altogether—the insects proliferate. When the mosquitoes feed on birds harboring West Nile, they can then transmit the virus to humans.

Helicopters in Illinois help track mosquito breeding grounds. In California, officials have begun looking to realtors to help. “They are our first line of defense because they are the first ones to find the neglected swimming pools that are virtually hidden from public view,” Contra Costa Mosquito and Vector Control District spokeswoman Deborah Bass told the Contra Costa Times on Monday.

California has struggled with this issue from the early days of the foreclosure crisis. Neglected swimming pools were associated with a 276 percent increase in the number of human West Nile cases during the summer of 2007, according to a study published this past November in the journal Emerging Infectious Diseases. In 2008, 445 cases of West Nile were reported in California, with the first case living next door to a stagnant pool, said David Farley, manager of the Fresno mosquito and vector control district. “The pool becomes an expensive toy, so a lot of people are just letting the pools go,” Farley told McClatchy in April.

The summer’s record-breaking rainfall in the Northeast, as well as depleting populations of bats that prey on mosquitoes due to white-nose syndrome, have increased fears as the U.S. enters its 10th West Nile season. “West Nile virus is here to stay,” Dr. Humayan Chaudhry, the health commissioner for Suffolk County, New York, told Newsday.

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