When I was a kid playing in the trough down on the farm we had both of these. The back swimmers used to hang out on the top, just beneath the surface, basking in the sun, their movements were more like moquito larvae. The boatmen looked more like a beetle to me and would zoom up to the surface, grab some air, and scoot back down to the bottom again.
We put little fish from the creek (cockabillies?) in there and they all lived happily for quite a number of years. I used to spend days playing in the trough all through summer... was only the bloodworms that used to gross me out!!!!
I hope this fascinating insight into my childhood helps you in someway!!! Oh the memories!!! sigh....