I call bullsh!t. Sprint 10 x 50m laps with 60 sec rest intervals. Then repost. Your whole body weight will have to be supported by the water, cuz after that you won't be able to stand up.
Swimming is BRUTAL. I was heavily in it as a kid. Never have I been so hungry as after 4 hours of swimming every Satruday morning. No football two-a-days or weight training session can even compare. All I wanted to do was EAT and sleep for the rest of the day.
And regarding fat swimmers - they are in a similar situation as the hour-a-day gym treadmill crew. Low intensity for a long time, so they are good at swimming. They make boats for that now, anyway.