Key Largo House circa 1997, next to Black Water Sound and MM 103. The original Mobile Home, now converted, bought in the early 1970s from the Eckart Family (left) and the two story home Donald built in 1980 (right). The original entrance to Cross Key Waterways on Black Water Sound at MM 103. Manatees love fresh water from a hose. Monroe County's GIS maps. A Key Largo Sunset September 25, 2009.