WEST PALM BEACH, FL (AP) Construction to strengthen the leaky earthen dike around Lake Okeechobee has been halted after problems with sand entering repair work.

Work on the project was halted in late May, according to an official with the U.S. Army Corps of Engineers. Engineers were trying to fortify the dike by cutting into it and inserting a clay material called bentonite, which expands when wet to form a barrier.

Steve Duba, the corps’ chief of engineering, said that the dike’s sandy nature created problems that weakened work being done.

“We call it a slowdown,” corps spokeswoman Nanciann Regalado said. “I can’t tell you how much the project will be delayed at this point. I can’t tell you how much the extra costs will be.”

The corps is considering other methods of embedding a 36-ft.-tall (11 m), 2-ft.-thick (0.6 m) concrete wall inside and under the dike, Duba said. The project had been scheduled to be finished in March and was supposed to be the first stage of a larger $300 million upgrade of the entire 143-mi.-long (230 km) dike.

Approximately 6,000 ft. (1,800 m) of work done by the corps’ contractor will now likely have to be torn out, Duba said.

The dike around the lake in the heart of Florida’s Everglades was built in the 1930s after a powerful hurricane and flood killed an estimated 2,500 people. It has been the focus of scrutiny since May, when state-commissioned experts found the structure is highly vulnerable to breaches caused by hurricanes and heavy rains.

The experts had criticized the repair project, saying that the work might worsen the dike’s leak problems.

The experts’ report prompted Gov. Jeb Bush to order state and local emergency managers to craft a mass evacuation plan for up to 60,000 residents living in the potential flood zone near the lake. Federal, state and local officials met mid-June to discuss the plan.