MINNEAPOLIS -- Feeling their way through the murky water of the fast-moving Mississippi River, deputies from three Minnesota sheriff’s departments on Friday methodically checked cars and trucks sunken in the collapse of the Interstate 35W bridge in Minneapolis.

Visibility underwater was limited to 6 inches as divers searched sunken vehicles previously identified by sonar, said Capt. Bill Chandler.

Chandler, a Hennepin County sheriff’s deputy, said the final searches of the vehicles amount to “pretty much a braille method” as divers feel for victims in the water. “Visibility is terrible. They can see maybe 6 inches at best.”

Divers were attached to a barge by a tether containing a communication line, which was played out one foot at a time to protect the divers and keep them from inadvertently going under the part of the bridge that is submerged.

Chandler said two divers were in the water at a time and two more were assigned to play out the tether and communicate with them. Because of the difficulty of the search, individual divers were allowed to be in the river for only about 30 minutes at a time. Communication was via microphones and “bone phone” hearing devices.

Chandler and Hennepin County Sheriff Rich Stanek said the search Friday was eased somewhat when the U.S. Army Corps of Engineers was able to limit the water being released through a dam at St. Anthony Falls and lowered the level in the search area by about 2 feet. The U.S. Army Corps of Engineers reported water in the river was flowing at 1,350 cubic feet per second.

Chandler, a diver and operations commander for the diving team Friday, said the work was difficult, dangerous and slow.

“Our divers take a lot of risks,” he said. As of Friday afternoon the diver teams had searched eight sunken vehicles and four partially submerged vehicles. No one was found in 11 of those cars and trucks. Chandler said the 12th was underneath another vehicle and could not be searched.

On Friday, the dive teams from Hennepin, Washington and Anoka counties were searching upstream from the collapsed bridge.

Chandler said sonar scanning of the river has identified six more sunken vehicles the divers planned to search.

Stanek said he did not know when crews with heavy equipment might be summoned to try to lift the bridge deck in the river.

The divers on the barge watched the underwater divers’ air bubbles and then directed the underwater searcher to the vehicles.

Stanek said he could not say what happened to the occupants of the empty vehicles – whether the drivers and perhaps passengers had escaped and swum to safety or drowned and are still in the river.

“There are windows down in the some of the cars, which allowed people to get out,” Stanek said.

In addition to the divers, crews from the Minnesota Department of Natural Resources have been patrolling the river and walking the river banks from the collapse downstream to the Ford Parkway dam, several miles downstream in St. Paul.

Of the eight completely submerged vehicles that divers have checked on Thursday and Friday, two were between the spans of the eight-lane bridge. One was downstream and five were upstream, Stanek said.

Chandler is a 28-year-old veteran of the Sheriff’s Department. He said that when the dive teams practice, they often do so with blacked-out masks, and sometimes they swim under the ice.

“This is by far the worst,” he said of the river conditions around the bridge.