The Red River of the North begins in Breckenridge, Minnesota, where the Otter Tail and Bois de Sioux rivers join, and winds 548.7 miles to Lake Winnipeg across a watershed of about 45,000 square miles, roughly the size of Ohio. Its depth and width vary by location and river stage: from Breckenridge to south of Fargo it is about 100 to 150 feet wide and can reach 10 to 20 feet deep, though mid-channel it is more often about 5 feet deep or less, while downstream of Fargo it grows wider and deeper so that by Grand Forks its width and flow have more than doubled and average mid-channel depth is around 10 to 15 feet, with holes up to 30 feet or more. Because the river channel drops only about six inches per mile across the former bed of glacial Lake Agassiz from 10,000 years ago, and because many tributaries also drain very flat watersheds, major periodic flooding results. Although its water often looks muddy from suspended fine clay sediment, the river is cleaner than about three-fourths of rivers in the continental United States; short-lived pollution spikes may come from storm sewers and runoff, municipal wastewater outflows are normally cleaner than the river water itself, and governments closely monitor water quality, which is not generally a major concern. Trees are scarce in the watershed because much of the region was tall-grass prairie before European settlement and because fertile flat soils were cleared for crops, yet the riparian forest along the banks provides habitat for native wildlife and a migratory corridor for birds. In the United States the river has eight dams, none navigable at normal water levels, and all but one lowhead dam have been retrofitted with rock boulders to reduce undertow and allow fish passage at nearly all water levels, with the remaining retrofit at Drayton, North Dakota, in the works. People have lived in parts of the watershed since just after the last glaciers about 10,000 years ago, while Europeans arrived only 400 to 500 years ago. Steamboats prospered on the river from about 1860 to 1909, carrying lumber, cattle, grain, people, whiskey, and other goods, until the railroad arrived in 1872 and gradually displaced both steamboats and Red River carts. People have long harvested fish and mussels from the river; in the mid-1800s Randolph Probstfield, the first European rural homesteader in Clay County, Minnesota, reported catching goldeyes to sell in town and to riverboat passengers, and native mussels were once taken for food, buttons, and jewelry, while zebra mussels are the latest invasive species to inhabit the river. After the river ceased to be the main transportation route it was neglected and even regarded as dangerous, but today it supplies municipal water, supports outdoor recreation, and was designated a Minnesota State Water Trail in 2001. Despite a common misconception, it is not unique in North America for flowing mainly northward, and North America also has at least 12 other rivers named Red River.