The St. Clair River serves as an international boundary between the United States and Canada and connects Lake Huron to Lake St. Clair. The river flows approximately 40 miles in a southerly direction from the outflow of Lake Huron to Lake St. Clair. Prior to entering Lake St. Clair, the river divides into several channels creating an extensive delta known as the St. Clair Delta/St. Clair Flats. The boundary of the St. Clair River Area of Concern is the entire river from Lake Huron to the southern tip of Seaway Island, west to St. John's Marsh and east to include the north shore of Mitchell's Bay on Lake St. Clair. The Beneficial Use Impairments are primarily due to intensive agricultural and industrial development in and near Port Huron, Michigan, and Sarnia, Ontario.