In essence, Riverkeeper is an environmental "neighborhood watch" group maintained by concerned citizens. Its constituents are not public officials and are not swayed by politics, but include members who defend the public use and restrict the private alienation of the river's benefits. Thus, Riverkeeper has engaged environmental justice issues, such as community park access. For example, around 1990, the City of New York Parks Commissioner restricted greenspace access by banning bus and subway transit, frequented modes of transport for African Americans, from reaching certain parks. Riverkeeper sued Westchester County and forced it to reopen six county parks that were closed to meet the budget, but due to their proximity to a railway, were mainly used by minority communities. The County had not closed any golf courses used by affluent residents, even though they were greater strains on County funds than parks that offered some minorities their only access to the river. This was not the only occasion where land use policies threatened the health of the Hudson River watershed as a public resource. In 1990, a team of Riverkeeper attorneys took on developers and lackluster enforcement agencies to protect the reservoirs and streams that constitute the water supply for nine million New York City and Westchester County residents. Riverkeeper also united with a chapter of the National Association for the Advancement of Colored Peoples (NAACP), in Ossining. During the 1960s, this oldest stable African American residential community in the Hudson Valley was rezoned industrial and has suffered social decline ever since. In 1991, Riverkeeper and the Ossining NAACP effectively sued the Ossining Planning Board to repeal an expansion of a construction debris processing plant that would have worsened diesel fumes and house vibrations at adjacent households.