Swimming back and forth in the pool is good exercise, but trying to swim against a current endlessly in one place is something else. The Pool Treadmill is a portable swim current generator that you place at the edge of your pool that produces 80 ft. lbs. of thrust and a 6 mph deep current without any turbulence. It's like an underwater treadmill for swimmers. I'm sure it's great exercise and all, but for $3,999.95 it would be cheaper to just go to the gym and get a personal trainer.
Pool Treadmill - Portable Swim Current Generator