After conducting research, it appears that the 4th Street boat ramp in Fairmount, Indiana is located on the Mississinewa River. The ramp is described as a concrete ramp with a width of 18 feet. It is open year-round and can accommodate a variety of watercraft, including motorboats, kayaks, canoes, and fishing boats.

According to the Indiana Department of Natural Resources, the Mississinewa River is a popular destination for boating, fishing, and other recreational activities. The river stretches for over 100 miles and passes through several counties in central Indiana. Anglers can expect to catch a variety of fish species, including smallmouth bass, largemouth bass, catfish, and crappie.

It is important to note that regulations and restrictions may vary depending on the specific section of the river. Boaters should always check with local authorities or the Indiana Department of Natural Resources for the most up-to-date information before embarking on any recreational activity on the water.