The National Park Service is criticizing plans to build four new bridges across the Congaree River and its flood plain, saying the work would damage wetlands and wildlife habitat near South Carolina’s only national park.

Congaree National Park superintendent Martha Bogle said in a recent letter the project would also clear forests in an area of Lower Richland being sought for expansion of the park.

The $25 million construction project would cover about four miles along U.S. 601, replacing a series of causeways and 1950s-era bridges with new causeways and bridges crossing the Congaree River flood plain. It also would replace the existing, deteriorating steel and concrete bridge over the river separating Richland and Calhoun counties.

Few people, including Bogle, have questioned the need for the new bridge across the Congaree.

But some government natural resource agencies and environmentalists want to bridge more of the flood plain approaching the river, which would eliminate the need for causeways that restrict movement of water and wildlife.

Monday is the deadline for challenging a federal permit request to fill eight acres of wetlands for the causeways.

The Park Service’s letter said the bridge project cuts through about 4,500 acres approved by Congress to expand the 22,000-acre Congaree National Park.

Park Service officials are trying to obtain land in this area and they anticipate “acquiring significant acreage adjacent to the U.S. 601 corridor in the very near future,” Bogle wrote in her July 29 letter to the U.S. Army Corps of Engineers, the nation’s wetlands permitting agency.

“I would not be doing my job as a National Park Service superintendent if I didn’t state some concerns as the project now exists,” she said Friday.

The S.C. Department of Transportation says it can’t afford more bridging across the flood plain. If the entire flood plain is bridged, it would increase the cost of the project to $75 million from $25 million, DOT officials said Friday.

Nearly two miles of the four-mile-long project would rely on causeways through the flood plain. The DOT plans to build new causeways when it shifts the bridge locations slightly west, then destroy most of the old causeways.

“We have to be very prudent with every dollar we spend,” said Berry Still, a project official with the DOT. “Without having somebody else come in here and defer that cost for us, it would be a humongous hit to the overall state budget.”

DOT officials say new bridges are badly needed to ensure motorists’ safety and the safety of boaters in the Congaree River. The state at one time posted signs under the main Congaree River bridge because of falling debris from the creaking steel span.

The main bridge over the river to Calhoun County is used by about 3,700 cars and trucks per day, the DOT says.

The Congaree River bridge project is the second major bridge proposal between Columbia and Lake Marion that has run into opposition in the past five years. The other, a connector between Rimini and Lone Star, has been challenged by outdoors groups and environmentalists because of its potential disruption of the Sparkleberry Swamp.

Still said the DOT would work with the Park Service. It might, for instance, install openings through the causeways to allow water — and animals — to pass under the road in the flood plain.

John Grego, president of Friends of Congaree Swamp, said the state’s proposal is disappointing. He had hoped to bridge the entire area to improve the scenery for visitors to Congaree National Park.

The park , established in 1976 as a U.S. preserve, is a federally designated wilderness area that contains the largest contiguous tract of old-growth bottomland hardwood forest in the country. More than 700 species of plants have been verified in the park, which also is home to alligators, wild pigs, snakes, turtles, bobcats, deer and a variety of bird species.

Reach Fretwell at (803) 771-8537 or sfretwell@thestate.com.