Brushpiles

is it legal to sink brushpiles in WI?

No it is not,you have to get a permit from the D.N.R., they want to no exactly where they are and become public knowledge. Granite

Well its legal in the sense that it can be done. They are called "fish cribs" in Wisconsin no matter the structure type (stakebed, boo-condo etc). You do need a permit. The crib must be placed by and maintained by a riparian.
The crib must be of a certain maximum size and a minimum depth of water, bottom content etc... There are forms that detail how to jump through all the hoops. I've been on some lakes that have cribs and they are not marked but the locals will mark them in some fashion. Others have a nice large buoy right in the middle with "fish crib" emblazoned on the side for everyone to see.

Now what you do under cover of darkness is your business and its between you & The Lord. ....And the game warden if he catches wind of it. :)

A Permit is usually NOT required in Wisconsin. Go to dnr.wi.gov/waterways/shoreline_habitat/fish_wildlife. It gives you all the info. One thing you must do is tell the local dnr office where the shelter/brush/crib is. Read the page I gave you, and ignore the other Bologna Sausage

Here is an updated link to the DNR checklist for shelter/brush/crib http://dnr.wi.gov/waterways/checklis...t_fishcrib.pdf