The Central Park Conservancy is a private, not-for-profit organization founded in 1980 that manages Central Park under a contract with the New York City Department of Parks & Recreation. Thanks to the generosity of many individuals, corporations, foundations, and the City of New York, the Conservancy has invested more than $500 million to date into the Park making it a model for urban parks worldwide. The Conservancy provides 85% of Central Park's $27 million annual operating budget and is responsible for all basic care of the Park. With 25 million visitors each year to its 843 acres, Central Park is the most frequently visited urban park in the United States. To manage the Park, Conservancy crews aerate and seed lawns; rake leaves; prune and fertilize trees; plant shrubs and flowers; maintain ballfields and playgrounds; remove graffiti; conserve monuments, bridges, and buildings; and care for waterbodies and woodlands, controlling erosion, maintaining the drainage system, and protecting over 150 acres of lakes and streams from pollution, siltation, and algae.