Divers will be back in the Mississippi River today, searching for victims of this week's Minneapolis bridge collapse.
Hennepin County Sheriff Rich Stanek says it's a dangerous job because the current going through the debris field is creating very strong man-made eddy pools.
In addition, the water is very murky, limiting visibility.
Stanek says crews have had indications from sonar of at least four submerged vehicles but divers haven't been able to reach them.
Meanwhile, the names of four people killed when the 35-W bridge collapsed have been released.
The dead are 32-year old Julia Blackhawk, 36-year old Patrick Holmes, 29-year old Artemio Trinidad-Mena and 60-year old Sherry Engebretsen.
Officials say as many as 30 or more people may still be missing, after the bridge collapsed into the river yesterday.
Search boats with sonar and two-man dive teams are taking a break while the water flow in the river is reduced at upstream dams.
First Lady Laura Bush will visit the site of this week's deadly bridge collapse in Minneapolis today.
While there, she will visit first responders and volunteers at an emergency command center.
The First Lady had previously-scheduled events in Minneapolis and the bridge visit was a late addition to her schedule.
President Bush will visit the area on Saturday.
He called the accident a "unique tragedy" that will be thoroughly investigated.
Bush pledged federal assistance to find out what went wrong and build a new bridge.
Meanwhile, the National Transportation Safety Board is classifying the bridge collapse as an accident.
A team of NTSB investigators is gathering statements from witnesses and analyzing security camera video, as well as images shot by journalists and the public.
The NTSB plans to reassemble some of the crumpled bridge on land to help determine what went wrong.
It will also use computer models in their probe.
At the same time, engineers are offering various preliminary opinions as to why the bridge buckled and fell, but are unanimous in saying this is not an isolated incident.
The American Society of Civil Engineers says thousands of bridges across the nation have defects or ar substandard.
The group estimates it will cost about 140-billion dollars to replace or repair damaged and obsolete bridges in the U.S.
Triple-A says a federal report finds that over 100-thousand bridges nationwide are either deficient for either structural or functional reasons, and the highest percentage of those bridges are in the Washington, DC area.
The federal report was compiled in 2005, and suggested that just over 63-percent of the more than 250 road bridges in the District are either structurally deficient or functionally obsolete.