Complex sentence: The park was established in 1934 when canal-building projects in South Florida were threatening the quickly vanishing Everglades, a network of wetlands and forests fed by a river flowing out of Lake Okeechobee into Florida Bay.
Split into simpler sentences: The park was established in 1934 when canal-building projects in South Florida were threatening the quickly vanishing Everglades. The Everglades are a network of wetlands and forests fed by a river flowing out of Lake Okeechobee into Florida Bay.