I am an open water swimmer, I find it more beneficial than stucking your head and focusing on finishing laps, and outdoors in my opinion always better. if the weather's right try this swimming workout:
warm up however you like then. We are aiming for maximum distance and energy output in each set..
5 sets of breast stroke, keep stroking
till max, and return to shore that completes a set
5 sets of free stroke, again stroke till
max distance and return to shore
5 sets of back stroke, keep stroking
to fatigue, no return journey.
5 sets of butterfly stroke, keep swimming to fatigue with breast stroke return as active rest.
as a finisher you can do 4 sets of combat side stroke, but thats an extra if you dont know the side stroke watch this video:
YouTube - US Navy SEALs Combat Swim
I like to do the combat side stroke at the end since I find it a good stretch for whole body. If you are interested in more swimming workouts then don't hesitate to PM me.