If you can exercise and explore at the same time, staying fit is so much more enjoyable.  A great example of this is inlet swimming. Inlets from the ocean often have tides which push water in and out.  We love to find an inlet and swim against the tide, it's great resistance and allows you to swim for a while but not move to far away.  There is always a risk when swimming in tides, you have to be very careful you don't swim above your capabilities and always have someone with you in case of trouble.  

One of our favourite inlets is at Red Rock, NSW, Australia.  The inlet has lot's of fish and meanders inland past a campground and the local park.  This one of our favourite ways to stay healthy and explore the local underwater wildlife.