HOUSTON -

A Marine Dense Fog Advisory was in effect Tuesday morning, forcing dozens of ships to remain docked or anchored until the weather cleared.

Houston Pilots, who navigate the vessels, suspended their service because of the low visibility.

"This has been a big tough fog season," said J.J. Plunkett, the port agent for Houston Pilots. "The latest stretch has been for four days. We suspended services off and on, but tried to get as many ships to pass through when there were areas of clear skies."

The Houston Ship Channel is a water pathway to one of the busiest ports in the United States.

"We normally move 50 to 60 ships a day," said Plunkett.

As a thick haze lingered along parts of the ship channel, traffic came to a stop.

"Monday, out of the 50-60 ships we were only able to move four."

Time is money for the businesses waiting on their cargo.

"When the port closes, it does affect commerce. It is estimated that every day ships cannot go through, there is a $489 million loss," said Plunkett.

In Deer Park, the dispatch office at Houston Pilots is staffed around the clock to monitor the weather conditions.

"We hope to open the port back up for ship travel, around 9 p.m., but that all depends on the weather. Safety is our main concern," said Plunkett.

Forty people within the port community will come together and identify priority ships that will be able to travel through the ship channel.

A ship becomes "high priority" based on its cargo.