Congress authorizes the C&SF Project providing for a network of more than a thousand miles of canals, levees, and water control structures throughout central and south Florida. These structures, along with previous attempts to drain and ditch the Everglades, reduced the size of the ecosystem by half in the last 100 years. Forty percent of the water that historically flowed into Everglades National Park is now diverted via canals to the ocean or for other uses. The Everglades has been further degraded by phosphorous, nitrogen, and mercury pollution from agricultural, industrial, and urban development. Exotic plant and animal species, many of which would never have been able to flourish in historic conditions, have further compromised the health of the system.