This was my first time on the Flat River. I started at Jackson's Landing Park right off Hwy 57 (Carson City Rd) just east of Greenville, spotted my car at East Riverside Park in Belding and rode my bike back to Greenville.
The sky was overcast with temps in the low 70's. The current was a lot stronger than I expected based on what I had read about the Flat River, at least for the first 2/3 of the 12-mile trip; Maybe because of the large amount of rain we have gotten recently. In any case it made for an enjoyable trip, especially through the Flat River State Game area. I only saw a group of 3 canoes and 2 fishermen in kayaks.
Approaching the dam in Belding, make sure you stay to the left to the portage. I made the trip in about 3 hours with only 1 quick stop to take a break along the way.
Nice access and parking in parks at Greenville and Belding
From Detroit area - take I-96 west to M66 north to Hwy 57
Decent river map posted at Jackson's Landing in Greenville