Au Sable River, MI

The Au Sable River in Michigan runs approximately 129 miles (208 km)[1] through the northern Lower Peninsula, through the towns of Grayling and Mio, and enters Lake Huron at 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.

It has a drainage basin of 1,932 square miles (5,000 km2)[3] and an average flow of 1,100 ft³/s (31 m³/s) at its mouth[1]. The river drops 650 feet (200 m) from its source at the junction of Kolka and Bradford Creeks[1].

The main branch of the river is formed near the border between Crawford County and Oscoda County where several branches come together. The North Branch headwaters arise in southeast Otsego County and flow south through Crawford County to merge with the main branch of the river. The Middle Branch headwaters arise in southwest Otsego County and flow south through Crawford County and Grayling. The South Branch headwaters arise in northeast Roscommon County and flow west through the town of Roscommon and then north and east to merge with the Middle Branch in Crawford County. The main branch 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. Twenty three miles (37 km) 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 fifteen miles (24 km) 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 mile (190 km) pro-am canoe race, the Au Sable River Canoe Marathon, which begins at 9:00 p.m. 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.

The Au Sable has about 350 miles (560 km) of tributary streams including the Pine River.