The U.S. Coast Guard continued late Saturday to scour the Mississippi River near Convent for a missing crew member of a tugboat that sank that morning.

The Coast Guard Sector New Orleans received a call that the UTV Miss Natalie sank near mile marker 163 about 8 a.m., the Coast Guard said in a news release. That part of the river is in St. James Parish, near Convent.

Ryan Tippets, a Coast Guard spokesman, said four crew members were rescued, but one was missing. He said none of the four rescued were injured.

It was unclear as of late Saturday what caused the tugboat to sink.

Tippets said there were no reports of extreme river or weather conditions in that area Saturday morning, and none of the crew had reported any problems with the boat to the Coast Guard.

A Coast Guard MH-65 Dolphin helicopter crew, divers and a sonar team were deployed to assist in the search, the Coast Guard said.

The Coast Guard restricted use of the river from mile marker 158 to mile marker 162 for most of the day to allow crews to search for the missing person.

Tippets said they anticipated opening the river for one-way traffic late Saturday, but he did not know what time that would occur. As of 7 p.m. Saturday, that portion of the river remained closed.

Tippets said there will be an investigation into what caused the tugboat to sink, and he said the Coast Guard might be the investigating agency, but he was unsure.