Orlando is mostly wetlands, consisting of many lakes and swamps. The terrain is generally flat, making the land fairly low and wet. The area is dotted with hundreds of lakes, the largest of which is Lake Apopka. Central Florida's bedrock is mostly limestone and very porous; the Orlando area is susceptible to sinkholes. Probably the most famous incident involving a sinkhole happened in 1981 in Winter Park, a city immediately north of downtown Orlando, dubbed ""The Winter Park Sinkhole".