Are you crazy? Shooting at the waters surface is just as dangerous (if not more) than shooting at the surface of the land. Bullets can and do glance off these surfaces and can travel upwards to over a mile away. I'm sure you're not interested in accidently killing someone over a muskrat. If you're going to shoot on the water, use a shotgun as others have suggested. Not a single projectile bullet, especially a 22 cal. People get shot and/or killed every year by stray bullets. Use common sense and make sure you have a solid backstop.A 22 works GREAT & helps sharpen the eye. Just follow them scooting near the surface & BAM. Done.
Some years back we shot 12 of them in a pond about 1 acre in size. We now have a annual shoot cause they keep comming back.
Nik