Ohh they are great swimmers !!
I put roxy in a nice big rubbermaid she she goes under the water and cruises around, but most of the time she swims with her head above the surface.
Just dont make the water too deep
I only make it about 2 times her hieght (like from her belly to her back) When i let her swim.Put somthing in there (like a rock or branch) so they can rest.