Complex sentence: However, long term average flow through the Straits is eastwards at around, in keeping with the main inflow to the system from Lake Superior through St. Mary's River in the west, and the main outflow through the St. Clair River in the east.
Split into simpler sentences: However, long term average flow through the Straits is eastwards at around. The largest inflow to the system is the St. Mary's River from Lake Superior, and the main outflow is the St. Clair River in the east.