Restoration of the Everglades
The Everglades, a region of tropical wetlands in southern Florida, are under an ongoing effort to remedy damage inflicted during the 20th century; it is considered the most expensive and comprehensive environmental repair attempt in history. The degradation of the Everglades became an issue in the United States in the early 1970s after a proposal to construct an airport in the Big Cypress Swamp.
Source: Wikipedia — Restoration of the Everglades (CC BY-SA 4.0)