Hey there @REI-MichelleW !
Spring in Michigan is the best. No wait all the time in Michigan is the best! Oh how I miss it! Here are my favorite water-based camping spots, organized by type of body of water!
Lake Michigan: A quick google search and you will easily find the most popular campgrounds along this coast, but I like Orchard Beach SP for a less crowded experience (though weekends will still be packed). You are also close to the Manistee River, which is high on my list of favorites in Michigan!
Multi-day River Trip: AuSable River - any of the Huron-Manistee National Forest AuSable River sites are great for more rustic camping, you can day paddle if you camp on one of the ponds. I'm a big fan of the campsite on the island (I thinks it's #84...). For more family friendly and traditional camping, check out Alcona Park.
Lake Superior: Whitefish Bay! Camp at Bay View Campground and from here you can get to Tahquamenon or St. Sault Marie easily and all the sites are right on the water. You literally are camping on a beach, we launched out canoe right from our site, it's about 5 miles to a little baby island you can picnic on. This is possibly my favorite drive-in campground in all of Michigan!
Lake Huron: The sunrise side is always beautiful and less crowded than it's western counterpart (check out East Tawas for amazing sunrises), but Port Crescent State Park is the best for paddling! You can head out to some really cool rock formations out of Port Austin and depending on how you drive home, you can check out some cool hieroglyphs on your way!
In-land Lakes: Everyone has their own favorite. Pick any of our lakes and you will love it for paddling. I'll let other folks chime in on theirs. Higgins Lake has always held a special place in my heart. And though on any of the larger lakes you will have to deal with speed boat wake, the Southern Campground has Marl Lake you can paddle in as well.