Municipal campground in Petoskey or the state park there are both on the water (bay). In the spring, it's going to be cool next to Lake Michigan. Petoskey has a great bike trail from the marina along the bay.
Ludington state park is good - lake and river to beach. Orchard Beach (north of Manistee) is up on a high hill - good view of the water from a few sites but no Verizon cell service the last time we were there 2 yrs ago. Hoffmaster was tucked in the woods near the beach (walking distance).
Liked Sleeping Bear Dunes too..
Most Michigan state parks have electric at the site. A few have full hookups.
Most important is what type of camping you like. (We like state parks)
Michigan state parks require a parking pass, check that out in planning. But that have lots of parks near water.