Why is it the "Red" River?
The \“Red,\” or Red River of the North, forms the border between North Dakota and Minnesota. It begins at the confluence of the Bois de Sioux and Otter Tail rivers near Wahpeton-Breckenridge, then meanders northward through Fargo-Moorhead and Grand Forks-East Grand Forks before reaching the Manitoba border near Pembina.
Source: prairiepublic.org