The Salt River is somewhat difficult to access near its mouth at the Tittabawassee, but it is possible. There is state land (marked as Pine Haven Recreation Area) along Saginaw Rd. west of Sanford that the river can be accessed from, or at the 11 Mile Bridge further down the road.
We put in from the state land for a 3.5 hr trip, taking out at Sanford Dam. The banks are steep with no formal trail, and the mud is very thick at the bank.
Beautiful scenery; bring lots of bug spray. Also be prepared to portage; we had to do so 4 times including one long one around a beaver dam. Poison ivy and nettle are abundant as well. The river is easy to navigate aside from the difficult portages, though it does get shallow in dry weather.