When Lead pipes were put in by the Victorians, many went straight to the pond/water pump. There is loads of agricultural lead piping about in fields, though most dug up for the scrap. They didn't know better. A load of farm ponds were filled in and might well include a few Lead batteries.

I think the legislation is either about fishing and Lead Shot, or about shooting wildfowl over wetlands.

You might get ricochets if you can get low enough an angle. Certainly a .22LR will.
The threat to wildlife or birdlife is slim. A .177 is a bit too big as bird grit! Wild ducks rarely live long enough to be effected by any Lead poisoning. The Lead would need to be highly concentrated and it would take exceptional circumstances for it to happen. Plenty of clay grounds have ponds where Lead concentrations are probably a tad too high; but can be sorted when dredged. Ask the Dutch as they reversed anti Lead legislation on shooting over water/in general. Plenty of daft science on the subject from Cambridge University!

Just watch the ripples for wind calls.