Ships were stopped again along the Houston Ship Channel on Tuesday evening after dense sea fog impaired visibility to unsafe levels in the 53-mile (85-kilometer) waterway between the Gulf of Mexico and the busiest U.S. petrochemical port, the U.S. Coast Guard said.

Vessel movement stopped at 6 p.m. local time (0006 GMT Wednesday) just five hours after ships had begun moving outbound from the port of Houston. Channel traffic was stopped from 3:23 p.m. on Monday to 1 p.m. Tuesday.

Ninety ships had been waiting on Tuesday afternoon to travel the Ship Channel, the Coast Guard said. Of that number, 30 were waiting to depart and 60 waiting to enter.

Navigation has been shut for more than 50 hours so far this week on the Houston channel. Fog cleared enough to allow ships to move along the channel for about three hours on Sunday as well as three hours on Monday.