They're an invasive species that was introduced as bait by some dumb angler, probably in the 1930s, from the Ohio River basin. They eat fish eggs, small fish, destroy fish breeding habitats, nibble on your toes when you're in swimming, and generally otherwise cause havoc (we were commenting that, as kids, the lake was full of clams - now there are only a few).
I never weighed what I got, but I was holding them in a 5 gallon bucket; it was about 3/4 full, in total. Two traps, each baited with leftover/rotten meat, pulled in in the morning and evening over six days. Threw 'em into boiling water, and drained them once the water came back to the boil.
They're found mostly in northern and Eastern Wisconsin. (Our area in Western Vilas County is among the worst.) Not sure netting would help catch them, though - the classic crayfish trap looks a little like a smaller lobster trap. Most hardware stores in the affected areas sell them for $10 or $15 each.