LAKE PONTCHARTRAIN, La. — Girder by girder, the 5.4 mile-long Twin Span interstate bridge across Lake Pontchartrain that was torn apart by Hurricane Katrina is being cut into suitcase-size pieces and turned into a fish haven on the muddy bottoms of the lake.

The artificial reef project is expected to become a popular fishing spot while helping restore Pontchartrain’s marine life and the health of the entire lake.

After decades of clam dredging, shipping, oil drilling and trawl fishing, vast areas of Louisiana’s coastal waterbottoms have been turned into sandy or muddy wastelands. At the same time, hurricanes and coastal erosion have undermined hundreds of miles of coast.

Any hard material is in high demand to stabilize sinking structures like roads and even old forts, harden shorelines and build artificial reefs in the swampy and gooey southern part of the state.

The nearest rock quarry in Louisiana may be in Winnfield Parish, not far from state’s highest point, Driskill Mountain, 200 miles from New Orleans. Most of the rock for jetties, rip rap and bank stabilization in south Louisiana is barged in from Kentucky, Illinois and Arkansas.

At one time, Lake Pontchartrain was underlain by a 6-foot bed of clam shells — but that was mined to smithereens and used to strengthen roads, railways and driveways. The same happened to mammoth reefs in the Atchafalaya River estuary to the west.

So the 1960s-era Twin Span bridge to New Orleans — being replaced by an $800 million new bridge — is viewed as a smorgasbord of rock.

“It’s popular material right now,” said Steve Heraty, an engineer with Volkert & Associates, a construction consulting firm overseeing the work.

For the past few weeks, machinery has been cutting up the bridge’s 25-ton concrete girders and spans, and welders have burned off protruding steel to ready the chunks for submersion.

About four acres of artificial reef will be made from 26,000 tons of bridge concrete, at a cost of $1.2 million. Tens of thousands of tons of concrete will be left over, and much of that will go into strengthening nearby shorelines, said Richard Savoie, chief engineer at the Louisiana Department of Transportation and Development.

The reefs will be next to the Twin Span between Slidell and the eastern swamps of New Orleans, near the Rigolets pass, a strait that connects Lake Pontchartrain with the Gulf of Mexico.

“A good portion of the lake filters through right at this corner,” said fishing guide Dudley Vandenborre on a tour of a reef site under construction. He steered his boat up to barges where concrete was being cut up and dumped in the water. Vandenborre has championed the idea of turning the bridge rubble into reefs.

“Before, it was a sand bottom, not much,” Vandenborre said. “When you’d dive, you’d see ripples in the sand, that’s all you’d see.”

The lake’s bottom wasn’t always sandy. It once was a rich environment of rangia clams built up over centuries.

Mike Poirrier, a biologist at the University of New Orleans, said a rangia clam population had begun to re-colonize the lake before Katrina, but the filter feeders were knocked out by a blanket of sediment and muck brought in by the hurricane.

“There are fewer clams now in Lake Pontchartrain than I have ever seen and the water is more turbid because of that,” Poirrier said.

The artificial reefs are expected to help the lake’s food chain from the bottom up.

“Marine organisms need something hard to attach to,” said John Walther, an artificial reef expert with the Coastal Conservation Association’s Louisiana chapter. “So, when you put the reef in there, it gives them that attachment — and that starts the food chain; the bait fish come; and then the speckled trout and the red fish are attracted to the bait fish; it creates a mini ecosystem.”

This being the Sportsman’s Paradise state, the aim is for this reef made from the rubble of Katrina to become a fishing hot spot.

“My grandfather fished when I was a little kid, and my dad. Everything I ever did has been associated with the outdoors,” Vandenborre said. “I couldn’t imagine doing anything else than being on the water.”

His story is common here in south Louisiana, where children are bred to love the water and memories are peppered with long sun-drenched weekends fishing. As Vandenborre spoke, a porpoise rolled in the distance and pelicans bobbed on the water.

The 56-year-old fishing guide pointed to a spot next to an older highway bridge where he caught a 10.5 pound speckled trout, the eighth biggest in the state’s record books.

“People are going to go for work in the morning, see all the boats (around the reefs), and say, ’I’m going fishing in the afternoon,”’ Vandenborre said. “Us here in Louisiana, when you see people fishing, or see a boat going down the road, you always wish you were with them.”