The Iroquois River originates in Indiana and flows in a northwest direction for 55.4 miles through Illinois to its confluence with the Kankakee River near Aroma Park. The drainage area of the Iroquois River basin is 2137 square miles with 1240 square miles in Illinois. With 11 named tributaries in Illinois, including Spring Creek (65 miles) and Sugar Creek (38.9 miles), the mainstem Iroquois River is a relatively low gradient, slow-moving river that is prone to diatom algae blooms in recent years. Like the Kankakee, the Iroquois River has not been channelized and retains much of its natural beauty, providing an aquatic resource of 2,547 acres.