When I was just a little girl my mother would always tell my sisters and I that we could not reenter the pool for 30 minutes after eating. This is 30 minutes less then the common belief, but still my sisters and I would sit by the pool for what seemed like ages waiting for my mother to say it was okay. As I grew older I still thought that I would get a cramp and drown should I not follow this rule. However, I few years ago my mother finally told me that this rule was simply a myth. Feeling like my entire childhood was a lie I decided to look further into this topic.
According to my sources it is possible to get a cramp in your stomach after eating should you partake in any physical activity. The body pumps blood to the stomach muscles when the stomach is digesting. It also pumps blood to the muscles used for swimming. Should their be a lack of blood flow to the stomach, the muscles can cramp. That being said, it is very unlikely to happen unless you eat a huge meal and then decide to do laps. Also, cramping does not mean that you will automatically drown. As long as a swimming does not panic they can float till help arrives or even work out the cramp.
It is unknown the origins of this myth but it was sighted in a 1968 film. Personally I believe my parents wanted to take a break from watching us in the pool after they finished eating. It was a good way to keep us out of the pool and out of trouble. When I have children at least I will not be so worried should they decide to jump in the pool before the 30 minute mark.