River all the way. Not talking huge rivers here but mountain rivers with boulders and stuff you can jump off into deep pools formed by currents. I remember being a kid and swimming at this park in the Oregon Cascades. I jumped off this big rock in the middle of the river and then turned around to swim back to it. I had a diving mask on and to my amazement the side of the rock was huge underwater and the side was all hollowed out. There were about 10 good sized rainbow trout just chillin’ in there. Almost as cool as that time I found that body under a pile of snags. Yep, rivers are the best!
I grew up on a lake (and live in Michigan) so that’s where I’m accustom to swimming. Now that I older most of the time when I go out on the lake we stand in the water drinking beer at the sandbar, it’s the party/hangout spot. If you go up north in Michigan they have crystal clear lakes, their very nice to swim in. People actually take baths in them from time to time too. But they have really big fish too. When I really feel like swimming I go to my best friends moms pool. I do like swimming in oceans to but there has to be other people swimming to, I watch shark week ever year.