Miami is known as "America's Cleanest City" for its year-round good air quality, vast green spaces, clean drinking water, clean streets and city-wide recycling programs. It also attracts millions of visitors with its beaches, conventions, festivals and events. The main portion of the city lies on the shores of Biscayne Bay which contains several hundred natural and artificially created barrier islands, the largest of which contains Miami Beach and South Beach. Miami Beach is home to a large number of beach resorts and is one of the most popular spring break party destinations in the world.