We are all well aware of the deteriorating conditions of our bridges above ground. We can see them.

But what about the conditions underwater?

Figuring that out is the job of the Massachusetts Department of Transportation dive teams, each made up of half a dozen divers who inspect more than 1,000 bridges every year. What they're looking for is the effects that river currents have on the bridges' foundations.

They demonstrated what they do recently at the Moody Street Bridge over the Charles River in Waltham.

Often, river water is so murky they can't visually identify problems, so they use a 3-foot-long aluminum "ruler" and some very bright lights to calculate the size of the bridges' footings and compare the results to past surveys. Wooden structures are susceptible not only to scouring by flowing rivers but also to insects, which can bore into pilings and cause severe deterioration.

After storm events when water levels can rise quickly, the teams are dispatched to bridges considered vulnerable. If severe erosion is found then bridges can be closed immediately for repair. But that hasn't happened in several years, in part because Massachusetts 3,500 bridges over water are inspected every three years. Five years is the federal requirement.

The dive teams are trained engineers who can spot problems before they become worse. And they dive all year round, not just when the weather is nice. The only thing they won't do, said team chief Randi Bonica, is go under ice. But he said they are busy year round and they inspect not only state bridges, but county and city bridges too — some of them dating back to the 1700s.

Although the water is still murky in many Massachusetts rivers, Bonica said in the 20 years he has been diving, water quality is definitely improving and it's becoming a bit easier to actually see what they're inspecting.