ANGOLA, La. -- Four Louisiana prison guards were in stable condition Monday after a collision on the Mississippi River in which a barge slammed into the boat that was ferrying the guards home after work.

The Coast Guard was investigating what caused the vessels to collide as the crewboat was taking workers who had just ended their shifts across the swollen river. Officials could not immediately say whether unusually high water levels on the river played a role in the crash.

In all, 18 workers from the state penitentiary were injured. Prison officials declined to identify the victims, but said four guards remained in stable condition at a Baton Rouge hospital on Monday.

The collision occurred at about 6:30 p.m. Sunday during a shift change at the sprawling plantation prison.

Normally, the Louisiana State Penitentiary in Angola uses a ferry to take workers and their vehicles back and forth from the west side of the river to the prison on the east side. But crewboats -- typically used to move workers to offshore petroleum platforms -- had been used recently because of the high water, prison spokeswoman Angie Norwood said.

James LeBlanc, secretary of the Department of Public Safety and Corrections, told The Advocate of Baton Rouge that the service would be suspended until river levels drop, forcing prison employees to find other means of travel.

The penitentiary, which consists of prison camps on an old plantation, has about 1,500 employees. About 40 percent of them live west of the river, according to The Advocate.

Prison warden Burl Cain said he would try using buses to bring workers across a bridge in Baton Rouge, which could be a four-hour trip.

"That's going to cause them not to want to come to work because you're going to work and ride 16 hours a day just to go to work," Cain told The Associated Press.

Still, operations at the prison were to continue as normal, he said.

Cain said the setting sun may have played a role in the collision.

"The pilot indicated that the sun was in his eyes and he just didn't see the barge," he said.

The crewboat had 20 people aboard, none of which went into the water, Norwood said.

The employees were first taken to the prison hospital, and 12 were transferred to other hospitals. The two most seriously injured were flown for treatment, Norwood said.

At Baton Rouge, about 40 miles downstream from Angola, the Mississippi River is expected to crest April 21 at 42 feet. Flood stage at that point is 35 feet, according to the National Weather Service.

Persistent heavy rains to the north have swollen the busy waterway, leading authorities to open a major spillway for the first time since 1997 in hopes of avoiding problems downriver.

River pilots had voiced worries about the high water, saying it's harder to anchor and navigate in the quick currents.

The Coast Guard had recently limited the number of barges that tugboats could push in the lower Mississippi.

Last month, a freighter ran aground near New Orleans and caused 60 nearby barges to break loose from their moorings. A stretch of river was also closed near Vicksburg, Miss., when a barge sank after hitting a bridge.

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Associated Press writer Sofia Mannos in Washington contributed to this report.

(Copyright 2008 by The Associated Press. All Rights Reserved.)