Every year one of my friends who is in his 60's and I go with a big group of people jet skiing down different rivers 150 plus miles. It is an easy ride, lots of turns, but mainly smooth sailing. Beautiful views and we get to go visit places like Cumberland Island that are accessible by water only. At the end of the day I am exhausted, and the next day usually my core is a little sore. If you have access to one of these water crafts and participate safely this can be a great exercise (expensive) but burns tons of calories. Burns around 240 calories and hour. Now we go for like 7 hours.. that is a lot of calories.
If you have never been, please participate with someone who is experienced and knows the safety precautions as it can be a dangerous activity. In high school I busted my ear drum knee boarding behind a jet ski. I was young and dumb. Now I am happy to just ride fast and have a smooth ride.
Whatever your style, have fun, stay safe and burn some calories!
Have a very fit day!