Alum 16.5 - could be schools of shad. I've seen a lot of marks on the finder that won't bite. I assumed crappie, but maybe not. Some fish on the bottom that may be walleye, or catfish, or carp.
I've also seen some other interesting objects - something that looked like a ladder or pier. Something that looked like an old farm foundation with a round ring (silo?). I few trees or fish cribs. I have a new hummingbird mega imaging side finder that lets you see some really cool stuff underwater, but I thought it would be cool to verify with an underwater camera, but if the visibility is only a foot or so it won't help.
This is from a boat in summer, not through the ice.