St Clair River, 64 km long, flows in a southerly direction, connecting Lake HURON in the N with Lake ST CLAIR in the S, and forms the international boundary between Canada and the US. Its northern portion has an average width of 0.8 km and depth of 8-18 m. In the S a delta called the St Clair Flats has formed, creating many channels and islands. The French were the first to explore and name the St Clair River.
SARNIA is the most important centre, deriving its industrial base from large petroleum refineries and petrochemical plants. These industries reported 11 chemical spills in 1985 and the discovery of a toxic "blob" on the river's bottom resulted in a $16 000 fine to Dow Chemical Canada Inc. The river is now monitored by Ontario's ministry of the environment. The banks of the St Clair are also home to many cottagers.