Like to know the zoning laws for Dover, MA

[FishermanTim]

I agree, no boaters were out, but they couldn't tell if anyone was hiking the area directly across from them.
The river at that area is 20-30feet across and the hiking path is a VERY short distance from that.

So besides the potential danger from a person and/or dog getting pelted with buckshot, there's also the pollution aspect.
They were shooting for at least a half hour, and had to be peppering the other shore and woods with a considerable amount of residue.

I'm not complaining about them shooting if it is legal, but just concerned about what they are leaving behind when they have finished.

[Slipknot]

many are concerned about lead, that is why there is steel shot and it is getting more widely used
lead comes from the ground anyway

I doubt it was buckshot
I have had birdshot land on me, it does not hurt it's more annoying than anything

you are right about knowing what is beyond your target, maybe they checked first maybe not