When you go into the water, the water goes into you too— into your eyes, nose, ears, mouth, and open wounds. Many state laws require beaches to close if tests show dangerous levels of bacteria. But Joan Rose, professor of water pollution microbiology at the University of South Florida College of Marine Sciences, studies another threat— viral infection— that usually goes unmentioned. Recreational waters off California, Florida, and other coastal states show surprising concentrations of viruses that can cause maladies ranging from gastrointestinal distress to possibly fatal myocarditis. Discover contributing editor Jack McClintock talked with Rose about the danger in the waves.