For a kid, nothing ruins the fun of a carefree summer day like a worried parent banning swimming right after the big cookout, fearing that the child will get cramps and drown. There is a slight chance of minor abdominal cramping, but for the vast majority of people, this isn't dangerous. The body does divert blood flow from the muscles to the gastrointestinal system to spur digestion, but not in amounts that diminish muscle function. Listen to your body and swim when you're comfortable -- just like you probably don't run a marathon right after Thanksgiving dinner, you don't want to start swimming laps right after a seven-course picnic. It's perfectly safe, though, to eat a light meal and then get wet. After all, athletes commonly eat right before competing.