BELGRADE – As brilliant morning sunshine warms the air over a central Maine lake immortalized in the movies, Jeff DeHart leans over the side of an aluminum boat and fixes a trained eye on a white buoy.

The bearded DeHart quickly spots a couple of long cracks across the bobbing cylinder, which have allowed Great Pond’s water to leak in since the ice went out. At the helm, Tim Thurston takes note of the damage.

“That buoy’s been in there since 1992,” says Thurston. “No wonder it’s tired.”

DeHart and Thurston are especially busy this time of the year, when boaters start to reappear on Maine’s inland waterways. The two are in charge of maintaining the state’s 1,275 navigational aids on 25 of its busiest lakes, including the one that provided the setting for the story that inspired the film version of “On Golden Pond.”

“We’re the buoy crew,” says Thurston, who, like his assistant, is wearing the state Conservation Department’s green uniform. “This is it.”

Their job takes on special significance this year, as DeHart and Thurston complete a federally mandated job that is also going on in roughly half of the states: Replacing some buoys with those bearing new colors.

The Transportation Department has mandated that lake buoys bear the same markings as those serving similar safety and directional functions in coastal waters.

“It’s so there will be one marking system, whether you are boating on inland lakes or along the coast,” said Thurston. “The buoys will have one meaning.”

The changes started last year, when 140 black-colored buoys used as channel markers in lakes were repainted green, consistent with the color of “cans” marking one side of coastal channels.

This year, 240 black-and-white striped buoys that mark center channels are being replaced by red-and-white aids, like those doing the same job along the coast.

The state had used red-and-white buoys to warn of submerged “points” or land extensions. Now, 270 of the old black-and-white buoys will do that job.

Other lake markings – such as a diamond for danger and a circle for controlled area – are already consistent with those that appear on buoys along the coast.

When he became familiar with the order to make buoy color markings consistent, Thurston noticed that the federal government didn’t have any designation to warn boaters to keep away from submerged points of land.

Thurston reckons the reason has to do with the way the lakes were formed. In other states, lakes tend to be man-made and are free of those hidden hazards.

But in Maine, glaciers, which left behind countless rocks and boulders, irregular land formations and other submerged surprises, gouged out many of the 5,800 lakes.

The federal government ended up adopting Thurston’s suggestion and made black and white the color designation for submerged points.

While the colors of coastal and inland navigational aids in Maine will match by the summer’s end, the shapes and sizes of the buoys will not.

State buoys are a standard 5-foot length of 9-inch-wide PVC pipe, filled with 10 inches of cement ballast and anchored by quarter-inch chain to 300-pound cement anchors.

Their coastal cousins – “cans” and “nuns” along channels and other various shapes and sizes – are larger and designed for much harsher elements. The Coast Guard maintains them.

Still, Maine’s smaller models are tough enough to stay put year-round. Most survive winter intact, although some take abuse from errant snowmobiles or get yanked off the mark by migrating ice slabs.

Thurston and DeHart spend the winter repairing damaged buoys in a Richmond workshop, where Thurston keeps track of each of the buoys on computer.

As the ice retreats, Thurston and his assistant are back inspecting buoys on lakes, generally from Sebago in the south to Moosehead in the north and Mooselookmeguntic in the west.

Outside of that range, associations granted permits from the state maintain buoys on 11 lakes. Some lakes may not be completely marked, and many are not marked at all. Their buoy colors are changing too.

To keep up with the work on lakes where they have buoy duty, Thurston and DeHart have to keep moving when the weather suits, logging hundreds of hours in the boat and thousands of miles hauling their boat and truckful of buoys over highways.

“In a normal season, we will replace about 170 buoys,” said Thurston. In a given year, about 15 percent of a lake’s buoys will need repairs or replacements, and about 2 percent of the total will disappear.

One reason buoys wander off is that the chains and shackles become weakened by rust, stress and wear, said DeHart, holding out a corroded steel link worn to the thinness of a pin. “This was holding a buoy,” he said.

Cottage owners are good about reporting missing markers, said DeHart.

“Once in a while, if they have a pet buoy in front of their camp and notice it’s missing, we get a call from them,” he said.

To help reunite any errant buoys that turn up in weeds or other hidden spots with their keepers, each has a small blue tag attached that lists the Conservation Department’s phone number, 582-5771.

Vandalism takes a small toll, one reason why Thurston and DeHart are on 21 of the lakes in their area every three weeks.