On an average day, more than 70,000 cars and trucks cross the Coronado Bridge suspended hundreds of feet in the air.
Inspectors make sure the roadway is safe and strong on top of the bridge but there's another crew doing important work underwater.
NBC 7 Investigates got exclusive access to the dive team, and their inspection reports.
"I"m going to duck under here, take a look around," Mitch Miller’s voice can be heard eight feet below the surface.
He’s looking for cracks and corrosion on the huge concrete pilings under the bridge.
"Making my way around," he said.
Five hundred pilings are driven deep into the muddy ocean floor.
They support 21 underwater piers that hold the roadway.
NBC 7 was there when the Caltrans dive team suited up for the most recent under-water inspection.
The 40-pound helmet is the most important piece of equipment.
"The big yellow one is the diver's breathing air," said diver Richard Hunt. "We also have a camera and a light."
Hunt, a veteran diver and civil engineer, monitors the diver's progress.
"This is the radio that we can talk to the diver through," he explains.
The diver narrates what he sees.
"He can put his finger up and say, 'Look at this." and "Look at this." and "Look at that" And we can record it and see it right on the camera," he said.
The divers use pretty basic tools like scrapers to remove barnacles and probes to measure the width and depth of cracks in the concrete supports.
Inspections like this are done every five years.
The divers work every-other-day, because the piers are cleaned before inspection.
That's a job for another crew using a high-pressure hose to blast off barnacles and other growth.
Records obtained by NBC 7 reveal results of the most recent Level II inspection in 2007.
The piers and piles were "in good condition with no major defects.”
"No sign of distress" was found, and cracks found during earlier inspections "had not changed in length or width."
But in 1996, divers did find problems with the concrete in Pier 19.
It helps support the longest span on the bridge.
Samples of the deterioration were sent to experts at UCSD.
They said there was no threat to stability on the span.
The dive team will inspect that trouble spot again in May.
“And trained people in the water, trained people on the surface, it's very accurate information and very detailed," Hunt said.
When deep cracks or rusted metal re-enforcement are found, they're cleaned and filled, much like a broken sidewalk.
The dive team keeps extensive notes, and a video and audio record, of these inspections.
So they can recheck any problem spots on their next dive.
A Level II dive inspection takes about six weeks, from one end of the bridge to the other.
The report from this current inspection will be available in in about two months.