This cache is not at the posted coordinates, and neither location is the Charlevoix River.
Okay, nowhere is there a Charlevoix River. That I found anyway. There is however a really long finger of a lake called Lake Charlevoix.
Lake Charlevoix is a lake in Charlevoix County in the U.S. state of Michigan. It is the third largest inland lake in the state with a surface area of over 17,200 acres and 56 miles of shoreline. The maximum depth in the main basin is 122 feet and in the south arm, 58 feet.
The lake's largest tributaries are the Jordan River, feeding into the south arm at East Jordan, and the Boyne River, flowing into the main basin from the east at Boyne City. Other significant tributaries include Horton, Stover, Porter, and Loeb Creeks. The outflow of Lake Charlevoix is the short Round Lake/Pine River complex which discharges into Lake Michigan at Charlevoix.
Young State Park is located on the shore of the lake just northwest of Boyne City. The Ironton Ferry at Ironton, a designated Michigan Historical Site in operation since 1876, crosses the south arm where it branches off from the main basin, saving about (at least) 20 minutes of driving time around the south arm by the shoreline route.
The lake was also known previously as Pine Lake and Long Lake. It was renamed from "Pine Lake" to its current name ("Lake Charlevoix") in 1926.
The cache hide is pretty much exactly what you'd expect for the location you will arrive at.