Environmentalists are out testing 20 waterways on the Delmarva.
The ShoreRiver Choptank Riverkeepers say that they have been testing for bacteria on the mid-shore and note that a lot shows up after heavy rains and thunderstorms.
Matt Pluta with the environmental group told WBOC that they had found a higher than the passing grade for bacterial even before the recent rains.
The Talbot County Environmental Health Department warned swimmers and boaters to be careful and wait at least 48 hours after a storm before going back into the water.
Pluta told the television station that he believes the problem may lie with failing sewer and septic systems that can contribute to an increase in bacteria.