There used to be one in the back Channel up by redwing I think. It mostly held those wet-sock fish though.
I fished one on Pool 5 once and did ok. Not sure how I found it, but now I can easily tell the difference between shells and just sand on my graph.
I think I fished one on Winnebago too. Had a few bites, but it was nasty on my line and I kept busting off when Id set the hook with a c-rig.
So, to summarize, yes I’ve fished them, yes they hold fish and no I dont know the best way to find them. I suppose I would look for areas that look like they are just sand and throw a crankbait around so you can feel what you are bouncing off of. If that fails, bust out your snorkel gear.