Number one: Get very consistent at making time in your schedule daily or at least a few times weekly and get out and do it. With water sports it can require more effort and organization than say tennis or running, bicycling or other sports. Since most of us don't live right at the beach or have a swimming pool in our yard, we have get to the water. If the water is cold we have to get into a wetsuit and other gear to be safe and comfortable. All the action and effort of getting your self out and organizing your gear combines with your sport to help you to lose weight.
Number two: When you are out there enjoying your sport, work hard at it, set some goals and increase what you can do in the time you have so you are working as hard as you can. To lose weight with a sport you have to push and play all out as much as possible. If you are doing your sport with a buddy or a team leverage off of them by having friendly competition.
Number three: Be sure you have the right sports gear for your specific sport. It is a lot harder to play all out if the gear you have is inadequate and holding you back. You simply can't get the most push for your effort which will not translate to trimming weight.
Number four: You have to eat correctly, I used to play the game with myself that if I really played hard and put out a lot of energy then I could or deserved to eat the comfort foods like junk food, desert or just simply foods that I know will put weight on my body. I erased the weight loss benefit of performing my water sport to the max. I finally got the message that it's always the combination of the exercise and the right food choices that lose weight and keep it off.
Number five: Having fun while I lose and then control my weight is what I call a win win. Doing a water sport or any sport for that matter and also lose weight is in my opinion so much better that struggling doing something you don't like and would otherwise not do. So I have as much fun as possible, I just work hard and eat right and I know I can control my weight on a sustainable basis.