The Au Train Falls information page from Chatham, MI says (in part):
The AuTrain Falls are part of the AuTrain River. A major reason why the falls were created is because of the large power dam located about a mile south of the falls site, in close proximity to highway M-94. The Forest Lake Dam, run by the Upper Peninsula Power Company, is the main source of water for the falls. When water levels are high on the AuTrain Basin, an increased flow of water is released via the dam and down the river. The AuTrain River actually flows from South to North. When more water is released via the dam, the more volume of water that flows through the falls.
…A short distance from the bridge, where the view is the most spectacular, is where an old brick building is located. As you approach the building, you will hear a humming noise and as you approach, the humming noise gets louder and louder. As you peak inside the building, you will notice these large lime-green mechanical devices. These are power generators. These generators create enough power to supply 600 homes in the area. The water to supply the generators also comes AuTrain Basin, but travels through large metal piping running from the Forest Lake Dam to the generator site. Once the water runs through the generator, it is released in the back of the building and back into the river. It is a unique facility, and one that is still an important part of the area.
Read on for more.