paths. The area contains a diverse selection of vegetation and other flora, which attracts a plethora of birds. At least 250 species of birds have been spotted in the Ramble over the years. Historically, the Ramble was known as a place for private homosexual encounters due to its seclusion. The Hallett Nature Sanctuary is at the southeastern corner of Central Park. It is the smallest wooded area at . Originally known as the Promontory, it was renamed after civic activist and birder George Hervey Hallett Jr. in 1986. The Hallett Sanctuary was closed to the public from 1934 to May 2016, when it was reopened allowing limited access. The Central Park Conservancy classifies its remaining green space into four types of lawns, labeled alphabetically based on usage and the amount of maintenance needed. There are seven high-priority "A Lawns", collectively covering , that are heavily used: Sheep Meadow, Great Lawn, North Meadow, East Meadow, Conservatory Garden, Heckscher Ballfields, and the Lawn Bowling and Croquet Greens near Sheep Meadow. These are permanently surrounded by fences, are constantly maintained, and are closed during the off-season. Another 16 lawns, covering , are classed as "B Lawns" and are fenced off only during off-seasons, while an additional are "C Lawns" and are only occasionally fenced off. The lowest-prioritized type of turf, "D Lawns", cover and are open year-round with few barriers or access restrictions. Watercourses Central Park is home to numerous bodies of water. The northernmost lake, Harlem Meer, is near the northeastern corner of the park and covers nearly . Located in a wooded area of oak, cypress, and beech trees, it was named after Harlem, one of Manhattan's first suburban communities, and was built after the completion of the southern portion of the park. Harlem Meer allows catch and release fishing. It is fed by two interconnected water features: the Pool, a pond within the North Woods fed by drinking water, and the Loch, a small stream with three cascades that winds through the North Woods. These are all adapted from a single watercourse called Montayne's Rivulet, originally fed from a natural spring but later replenished by the city's water system. Lasker Rink is above the mouth of the Loch where it drains into the Harlem Meer. South of Harlem Meer and the Pool is Central Park's largest lake, the Jacqueline Kennedy Onassis Reservoir, known as the Central Park Reservoir before 1994.