The Au Sable is a major tributary to Lake Huron. It drains a north-south basin that includes 1,932 square miles in north-central lower Michigan. The basin is approximately 90 miles long and 10 to 30 miles wide. The river basin is partially within the Huron National Forest and includes parts of Otsego, Montmorency, Crawford, Osco, Alcona, Roscommon, Ogemaw, and Iosco counties.
While technically a part of the Au Sable River Basin, many observers view the Pine and Van Etten Creek Watershed in Iosco and Alcoa counties as a separate, distinct river basin. This is due to the fact that the Pine River system drains into the large Van Etten Lake before entering the Au Sable River less than two miles from where the main river drains into Lake Huron.
There are approximately 476 miles of streams in the Au Sable River system. The mainstream is about 129 miles long and includes 37 miles of impoundments. The table on page 6 is a list of streams within the watershed (a few small unnamed streams are not included). Lengths are shown in miles. Au Sable Natural Rivers Map
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Main Stream - Source to Mio - The river follows an occasionally narrow, sinuous course before straightening at McMaster's Bridge. It has sufficient depth for canoeing at all seasons, but heavy ice may be encountered above this area during severe winters. There are many short sections of fast riffle current, sharp turns, and occasional sweepers and down debris which constitute challenging and relatively safe floating for the novice and beginner canoeists.
Main Stream - Mio to Alcona - This 23 mile segment was the only portion of the Au Sable River system designated by the U.S. Congress as a component of the Federal Wild and Scenic River system. From Mio to Alcona Pond, the river has occasional large curves and many short relatively straight stretches. The river is wide, flows at a moderate speed, and has sufficient depth for safe, pleasant canoeing by beginner-novice level canoeists. It is free of all debris and sweepers but may be iced over below McKinley during severely cold winters. There are occasional short stretches of riffle.
Main Stream - Alcona to Mouth at Oscoda - Below Alcona Dam, the Au Sable flows through many large gradual curves with few straight stretches over 1/4 mile long.It is a large river at this point and has sufficient depth and width for easy canoeing. However, during power generation discharge at Alcona, the water level may rise up to four feet and create somewhat hazardous conditions for inexperienced canoeists. Although this section is relatively free of debris, the current becomes quite strong forming deep eddies and some turbulence. Conditions similar to those below Alcona also prevail below Foote Dam. However, the lower river has considerable amounts of sunken and partly submerged debris which is largely covered during high water.
South Branch - The South Branch above Roscommon follows a slow sinuous course through lowlands. The channel is narrow and frequently choked with downed trees, debris, and overhanging shoreline vegetation. Although safe, it is arduous, slow and unattractive to most canoeists.Below Roscommon, the river has adequate depth and width to provide safe, pleasant canoeing experiences. It has many gentle bends, several narrow channels and many short interesting stretches of riffle. It is relatively free of debris that would hinder canoeing, but may have several shallow tretches with exposed rock during very dry seasons.
North Branch - The North Branch above Lovells progresses from a slow, narrow meandering stream, clogged with shoreline vegetation, to a much wider shallow river at Lovells. The vegetation, debris and shallow water make this section very difficult to navigate with a canoe. Below Lovells, the first 1/2 mile may be shallow and difficult during normal seasons but can be floated safely. The lower river has adequate depth and width for canoe use.