Hello:
Sure they can, or at least mine could. I was walking in a park with a stream + ducks in it and I let Nik off the leash to run around. I did not think about the water or her going in it!!! WRONG!!! She went like a rocket and dived in to chase her enemies, the ducks LOL. She swam along with them and I had to get wet and pull out this bedraggled, dripping (with reclaimed water!!!), yorkie and carry her to the car. I had to put her on the floor and wash her immediately when I got home as goodness knows what was in the water.
So YES they can swim as I found to my cost. So hang on to them when near water!
