Lemme get this straight - you were shooting a centerfire out to the water on a public/navigable lake? You're lucky you did NOT get arrested, and/or chewed out more by more people, if that's the case. If that's what you were doing, I would have done the same or worse. You ever heard of a ricochet? Just MO. I was once young (meaning under 25) and would have done the same thing at one point, but we all can and must learn when we are doing something stupid - somehow; sorry.
P.S. You did a great job and handled it correctly, once the confrontation started. Just next time, do one even better and don't do the stupid thing that caused the confrontation. Use an earth backstop / burm which is located on your private land, or don't shoot. It's that simple.
Good point. If this was in fact on a navigable lake, I might tend to change my opinion to that of the doctors. If you were shooting on a small flood control lake/pond with no access by anyone else and a very densely wooded area surrounding area, you were ok. It's never a good idea to shoot at water anyway. Which type of waterway was this?