"...looks to be Daisy Red Rider BB guns..." Winchesters and Brownings. 1895's. That picture was in one of the gun rags years ago. There was all kinds of assorted now collector grade stuff, in collector grade condition, pitched into Lake Michigan. There's a spot off the Toronto Islands that scuba divers are not permitted, with a PDQ reaction by Harbour Police if you try, to dive for the same reason. Wasn't just firearms in Chicago though. Slot machines too.
"...aircraft come out ok..." Al doesn't corrode the same way steel does. Fresh water causes rust just as quick as salt water. It's about the amount of oxygen that matters. That's about depth.