This is a great question and one that is best answered by the MN DNR. If you are wondering whether or not you need a permit for your dock system, we recommend that you take a look at the MNDNR General Permit 2008-0401. The information in this article is borrowed from the MN DNR website.
Docks and Access in Public Waters
Docks, those narrow structures used for getting to deeper water, are commonly used on Minnesota lakes and rivers. For many docks, no permit is needed to install, construct, or reconstruct on shoreline property. For certain docks, a general permit may be used. There are many options, and we recommend that landowners use the smallest and narrowest dock that will reasonably meet their water access needs.
Do I need a permit for my dock?
How to Use General Permit 2008-0401
If the requirements of General Permit 2008-0401 are met, a dock platform is automatically authorized under this permit. There is no need to print a form or send in an application. If your dock platform meets the requirements of this general permit, no further action is needed.
Restrictions On Docks
You may not place a dock in public waters if the dock: