Fun thread!
We did an underwater clean-up dive maybe 10 years ago in a shallow bay popular with recreational boaters in the summer. Pulled up gas grills, cocktail glasses, and all kinds of stuff that fell overboard. Can't remember how many pounds of stuff we pulled up.
Before moving here, we also used to do drift dives in the St Clair River south of Sarnia, Ontario, and it was not unusual to find ship china and fragments on those dives. White Star Line was the stuff I saw most often.
Some of my coolest finds were not underwater, but digging in an old abandoned oil well dating from the mid to late 1800s. Once the oil well stopped producing, it became a late Victorian garbage dump. In the mid to late 80s, we'd always find tons of old medicine bottles, soda bottles, liquor bottles, ink wells, spittoons, children's toys, etc. Bits of oil still seeped up, so it was messy and smelly and it took forever to clean up our finds. Most are still in my dad's attic, I think, and emptying that attic will be one of my fall chores. Can't wait to re-find it all again. My wife will love it when more boxes of "treasures" show up here (instead of staying there)...