MINNEAPOLIS - The command center is a jumble of trailers, tents and canopies, the impromptu infrastructure of a recovery effort that has shifted from frenzied to plodding. Behind the zealously guarded perimeter, cops, investigators and divers struggle under a scorching sun to find the last victims of the interstate bridge collapse.

Tons of shattered concrete thrust upward from the Mississippi River a few feet away, and tangles of rebar and more concrete remnants hang overhead. There are moments of levity in this gloomy work, but they do not last.

"Somebody will crack a joke, but then you'll see someone turn back and look for a second, and you see it in their eyes," said Lisa Fleming, a photographer for Hennepin County who's been documenting the work at the collapse site. "They get quiet, and it all comes back."

Heavy cranes stand ready to haul away the rubble, but they're only occasionally summoned to hoist a car or truck in the divers' way. The top priority here is finding the missing - a number that stood at five on Saturday, when swift currents fed by an overnight rainstorm kept divers out of the water for a few hours.

When remains are pulled from the water, officials call for a moment of silence. Only workers needed for the removal are allowed to be present, and all other work on the site stops.

"There's a sanctity they want to provide," said Carolyn Marinan, the chief county spokeswoman, who's spent time at the site. "They know that there are people who have loved ones in there, who are waiting to know that they can close a chapter."

Navy divers are leading the search for bodies, two teams of eight or nine each working in 9-hour shifts.

They struggle to penetrate a highly unstable debris pile, sometimes swimming tethered to a surface air supply, sometimes shifting to a helmet and no more than a snorkel in the tightest spots.

The stretch of river under the bridge is muddy and shallow, only 2 to 14 feet deep. Hot, humid weather has gripped the city during most of the recovery operation, and the warming Mississippi saturates the air with a musky river scent.

"This is probably one of the more difficult scenarios we've dealt with," said Navy Senior Chief Dave Nagle, the spokesman for the Navy dive team.

When they're in the water in their head-to-toe wet suits - heavy canvas and denim to protect them from jagged concrete and steel - divers use radios in their helmets to communicate with other divers on shore acting as their safety tenders. The tenders in turn talk by radio with the diving command team, just up the river bank in a trailer.

The divers don't complain, says Tim Mares, the Army Corps of Engineers' manager of the nearby lock and dam operation, where some command center operations are now based.

"These young guys, they just go about their mission and when they have down time, they stay to themselves," Mares said. "They don't want to lose focus on anything but doing the job."

The diving operations have been starting early in the morning and going late into the night. Nagle said the divers who come off the clock go elsewhere to sleep to make sure they get the rest they need.

There's a lot of other activity at the site as well - sheriff's deputies and police officers keeping a tight clamp on security, investigators from the National Transportation Safety Board and the state of Minnesota, Army Corps officials and assorted other local, state and federal officials.

"There's a lot of people, but they're just very somberly going about their business," Mares said. "People move with purpose."

Many at the site are working 12-, 14-, 16-hour days, constantly on their feet and often in the sun. Much of the area is covered in river mud. "After a full day there wearing heavy shoes and socks, I'd take them off and my feet would be black, just filthy," Fleming said.

The Red Cross brings in three meals a day, along with lots of bottled water and snacks. Wal-Mart shipped over boxes of other essentials like aspirin, toothpaste and toothbrushes, lip balm and sunscreen, though perhaps too late for some regulars at the site like Hennepin County Sheriff Rich Stanek, who was tanned deeply by the end of the week and appeared to have lost weight.

Families of the victims visited the site in two groups the weekend after it collapsed. They haven't returned, but they have kept in close touch with the workers there, sending care packages of food and a banner to fly at the water's edge.

"They are very gracious about the pain they are suffering," Stanek said. "You look into their eyes and they look back, and they very much care."

Though many different agencies are on site, people close to the operation say there's no jurisdictional squabbling. They describe a sense of camraderie and shared purpose.

"I've worked a lot of disasters," said Shannon Bauer, an Army Corps spokeswoman who's spent time along the river. "This one's no different. You get to be pretty good friends with the people that you're working with nose to nose 15 hours a day."

Many who've spent time at the site say it feels surreal. The vast scale of the damage and the unreality of the surroundings - huge bridges don't just collapse - "make you feel like you're on a movie set," Fleming said.

Marinan, the county spokeswoman, said she found herself noticing odd things.

"There were all these pigeons flying around the bridge remnants, and I realized they didn't know where they're supposed to go anymore," she said. "I thought, what a goofy thing to say out loud. But I was talking to this burly cop, and he said the same thing."