Chances are, at this very moment, a family is arriving at some U.S. shoreline ready to spend a week relaxing at the beach. But before mom, dad and the kids can get their feet warm in the sand, a sign confronts them: "Beach closed. No swimming allowed." As the children slouch back to the car, a parent tries to console them. "At least the hotel has a swimming pool, and there's always next year." And so it goes. Similar routines are played out for real thousands of times each year in this country. And the culprits — those who...