The Au Sable River is a 138 mi river in the Lower Peninsula of the U.S. state of Michigan. Rising in the Northern Lower Peninsula, the river flows in a generally southeasterly direction to its mouth at Lake Huron at the communities of Au Sable and Oscoda. It is considered one of the best brown trout fisheries east of the Rockies and has been designated a blue ribbon trout stream by the Michigan Department of Natural Resources. A map from 1795 located in the United States Gazetteer calls it the Beauais River. In French, the river is called the Rivière au sable, literally "Sand River".

Description

The Au Sable has a drainage basin of 1932 sqmi and an average flow of 1,100 ft3/s (31 m3/s) at its mouth. The river drops 650 ft from its source at the junction of Kolka and Bradford Creeks. The main stream of the river is formed at 44.80583°N, -84.75806°W in Frederic Township in Crawford County by the confluence of Kolke and Bradford Creeks, which both rise in Otsego County. The river flows south then turns east through Grayling, where it is joined by the East Branch Au Sable River at 44.66528°N, -84.70361°W. The East Branch rises in Lovells Township, Crawford County at 44.82944°N, -84.59972°W. The Au Sable continues eastward and is joined by the South Branch Au Sable River at 44.65639°N, -84.46833°W in South Branch Township. The South Branch rises out of Lake St. Helen in Richfield Township, Roscommon County at 44.38167°N, -84.44389°W and flows northwest into Roscommon then northeast to the main branch of the Au Sable. The North Branch Au Sable River joins within approximately 5 mi in eastern Crawford County at 44.67056°N, -84.38083°W near the boundary with Oscoda County. The North Branch rises in Bagley Township, Otsego County, near Lake Otsego. The Au Sable then flows mostly east through Oscoda County, then south and east through Alcona County and Iosco County. The river's watershed also drains portions of Montmorency County and Ogemaw County. Most of the main branch of the Au Sable flows through or adjacent to the Huron-Manistee National Forest. 23 mi of the river, from the Mio Pond downstream to the Alcona Pond, was designated as a National Wild and Scenic River on October 4, 1984. The watershed provides habitat for bald eagles and the endangered Kirtland's warbler. Five percent of the land in the watershed is National Forest and 29% is state forest. It is a designated trout stream, and many canoe liveries exist along the river, which offer canoe trips from a few hours to as long as a week. The river was originally a grayling fishery with brook trout being released in the 1880s. By 1908 the grayling were gone although they were reintroduced in 1987. (See Grayling, Michigan, for more information on the Grayling and the fish hatchery.) Brown trout is the current main catch. The Lumberman's Monument, in honor of the lumberjacks that first populated the area, is located on the river about 15 mi west of Oscoda. Lumbering along the river began in the 1860s and was finished by the 1910s. The Au Sable River is also the site of a yearly 120 mi pro-am canoe race, the Au Sable River Canoe Marathon, which begins at 9:00 p.m. on the last Saturday in July, and runs through the night into the next day. Winning times have ranged from 14 to 21 hours. The race was first run in 1947. River Road, running parallel with the Au Sable River, is a designated National Scenic Byway. There are six hydro-electric power plants in the Au Sable River basin, with a total installed capacity of 41 MW and an average annual energy output of 500 GJ. The six reservoirs were constructed between 1911 and 1924. The Au Sable has about 350 mi of tributary streams including the Pine River.

Towns along river

River dams

Ordered from upriver to downriver, all belonging to the power company Consumers Energy:

Historical markers

The river has five historical markers on it:

River valley attractions and events