Section 207.425 - Calumet River, Ill.; Thomas J. O'Brien Lock and Controlling Works and the use, administration and navigation of the lock(a)Controlling Works.(1) The controlling works shall be so operated that the water level at the downstream end of the lock will be maintained at a level lower than that of Lake Michigan, except in times of excessive storm run-off into the Illinois Waterway, or when the lake level is below minus 2 feet, Chicago City Datum.(2) The elevation to be maintained at the downstream end of the lock shall at no time be higher than minus 0.5 feet, Chicago City Datum, and at no time lower than minus 2.0 feet, Chicago City Datum, except as noted in paragraph (a)(1) of this section.(b)Lock - (1)Operation. The Thomas J. O'Brien Lock and Dam is part of the Illinois Waterway which is a tributary of the Mississippi River. All rules and regulations defined in § 207.300 , Ohio River, Mississippi River above Cairo, Illinois, and their tributaries; use, administration and navigation shall apply.40 FR 57358, Dec. 9, 1975