I saw broken bottles underwater at a popular Lake Superior swimming spot in Duluth. A few days later I was able to return and used my powers for good to clean up after the bad guys. You can either wade in at the shallow end of this spot, or rock-jump in at the deep end, either way there was broken glass within reach of innocent bare feet. It was the remains of at least five separate beer bottles, probably from one douchebag at a party of cowards.
I spent about three hours collecting all the glass I could in dives lasting 30-45 seconds each with rests to catch my breath in between. I couldn’t get it all, there were many shards too small to pick up, but they will wash away most easily into the deep. All of it would have turned into smooth beach glass sooner or later, or been sucked out to sea by the next storm, but in the meantime this mess sat there for several days and could have easily lacerated someone. I was very careful picking it up, but obviously it was a little risky and the wave action was moving me around quite a bit (good thing my Atlantean physiology is adapted to the pressure at great depths, so my skin can even resist machine gun fire).
Be warned: I protect this lake, and those who come here. If I catch anyone breaking glass at the beach I will not hesitate to call the police. Either that or I will telepathically summon a giant catfish to eat you.
Local news spot here.