Is swimming immediately after taking meal injurious for health ?

No, current medical evidences do not suggest any harmful effects of swimming after having food. However if you are planning to swim as a form of exercise, its better to wait for about an hour so that the food in stomach has been digested. Vigorous exercise may lead to muscle cramps and stomach aches at times.

The belief that if you swim within 30 minutes after having meals or food can lead to stomach cramps and may even lead to drowning was based on the premices that after we take food, the blood supply in the body is diverted ot he stomach to help for digestion and if you exercise at the same time, the blood would be diverted to the muscles. This would result in decreased blood supply to stomach leading to harmful effects. 

But the fact is that body has enough reserve of blood and oxygen to meet the increased demands of the stomach and the muscles used in swimming. 

In case you are planning for swimming as a form of exercise or doing vigorous compititive swimming, it is advisable though to postpone such exercise for at least 30 minutes to an hour after taking heavy meals.