The U.S. Gulf Coast’s most important industrial waterway partially reopened on Monday after it was polluted with cancer-causing benzene and toxic runoff from the region’s worst chemical disaster in more than a decade.

A two-mile (3.2-kilometer) stretch of the Houston Ship Channel’sthat’s been closed for three days will be open during daytime hours while the clean-up continues. Pilots have been ordered by the U.S. Coast Guard to stay at least 40 minutes apart so each vessel can be inspected...