Contractors are suing the South Florida Water Management District after it terminated their contract to construct the half-billion-dollar Caloosahatchee (C-43) Reservoir in Hendry County, Fla., contending that design changes and other actions by the agency caused delays, not the firms' performance.

C43 Water Management Builders, a Lane Construction Corp.-led joint venture with its Italy-based parent Webuild SpA, filed the lawsuit in the U.S. Southern District of Florida Court against the district, charging it with wrongfully terminating the almost $524-million contract.