Both my guys can swim. We visit my in-laws' home on the lake every summer - and we throw the ball into the water - Wylie flies into the water, swims out to fetch - he LOVES to swim in the lake. Marcel fetches Wylie. Marcel can swim just fine - but even a small wake on the lake can go over his head (he's 3 lbs). We have a pool at home, and they don't really like it as much - probably the smell/chemicals.
