Marsh Creek becomes the Middle Fork Salmon where it joins together with Bear Valley Creek.
Kayakers or other small enough craft can launch at State Highway 21, float down Marsh Creek to where it becomes the Middle Fork Salmon and on to the big raft launching facilities at Boundary Creek. Permits are required if boaters continue on the Middle Fork below Dagger Falls/ Boundary Creek. This launch is typically used in the early season when snow blocks access to the Boundary Creek put in.
Other Information Sources:
Four Rivers Permit Information forest service page
Floating the Middle Fork of the Salmon River, Forest Service page with intro video.
Middle Fork Salmon; forest service information - very comprehensive
Idaho, the Whitewater State, G. Amaral (Watershed Books; 1990)