When it rains in Georgia, you may want to buy your peaches in a can.

Researchers at the University of Georgia in Athens (U.G.A.) have found that rain ups the risk of salmonella in rivers and streams—and, in turn, in products nourished by and washed in tainted runoff waters. The scientists report in Applied and Environmental Microbiology that 79 percent of water samples from rivers and streams in southern Georgia collected and tested over a year contained the rod-shaped bacteria; concentrations were highest in specimens gathered in the summer months and right after it rained.

Study co-author Erin Lipp, an associate professor of environmental health sciences at U.G.A.'s College of Public Health, says the findings indicate that officials trying to trace the source of salmonella contamination should put untreated surface water at the top of their suspect list.

After a downpour, rainwater accumulates on ground surfaces or in bodies of water. Before it reaches a final destination, the surface water may come into contact with salmonella—which lives in the intestinal tract of humans and animals and can be spread via their feces and vomit. Contaminated water may seep into porous soil—and thereby infiltrate irrigation systems used to nourish fields and wash produce.

"If the [tainted] water is used to irrigate crops, it would likely contaminate the crops," says Michael Doyle, a professor of food microbiology and director of U.G.A.'s Center for Food Safety who was not involved in this study. In fact, polluted water used to irrigate or clean produce has been linked to several well-publicized outbreaks of salmonellosis, the infection caused by salmonella, in recent months. Alfalfa sprouts were recalled in January, and have been linked to more than 100 cases of salmonella poisoning in four Midwestern states. In late March, 50 illnesses and 14 hospitalizations were tied to salmonellosis caused by consuming Honduran cantaloupes. Outbreaks were reported in 16 states, including Georgia.

The researchers decided to probe Georgia's waterways and rainfall given the state's unsavory history with salmonella. Most recently, federal health investigators tracked a nationwide salmonella outbreak to peanut butter and paste sold in bulk and used in baked goods and crackers produced in a Peanut Corporation of America (PCA) plant in Blakely, Ga. The U.S. Food and Drug Administration (FDA) has linked nearly 700 illnesses (and possibly nine deaths) to peanuts hailing from that site. In that case, the major source of poisoning is believed to have been a combo of filthy conditions and a leaky roof through which rainwater laced with contaminated bird feces dripped onto the peanuts in the facility. (Last week, PCA was fined $14.6 million.)

Just two years earlier, a ConAgra plant located in Sylvester, Ga., recalled its peanut butter products after reports of salmonella-related illnesses were traced back to it. A leaky roof was also blamed for salmonella contamination of their goods.

Many counties in Georgia produce both poultry and peanuts. Blakely, home to the infamous PCA plant, is the number one peanut producer in the nation. The state is also the country's top poultry exporter. Some farms in Georgia produce peanuts and export poultry simultaneously.

Producing these two disparate products in close quarters exposes goods, like peanuts, to a microorganism that they would not encounter under normal sanitary conditions.

The most recent salmonella recall involves pistachios: Setton Farms in Terra Bella, Calif., the country's second-largest pistachio distributor, recalled two million pounds (907,000 kilograms) of the nuts last month after some were found to be tainted with salmonella. The FDA has advised consumers to avoid pistachios until further notice.