| Lake Hopatcong | |
|---|---|
 At sunset, seen from Bertrand Island | |
  Lake Hopatcong  Lake Hopatcong  Lake Hopatcong  Lake Hopatcong | |
| Location | Morris / Sussex counties, New Jersey, United States |
| Coordinates | 40°57′N 74°38′W / 40.950°N 74.633°W |
| Type | natural lake, reservoir |
| Primary inflows | Weldon Brook, Unnamed Streams, natural spring |
| Primary outflows | Musconetcong River |
| Basin countries | United States |
| Max. length | 9 mi (14 km) |
| Max. width | 800 ft (240 m) to 1 mi (1.6 km) |
| Surface area | 4 sq mi (10 km2) |
| Max. depth | 50 ft (15 m) |
| Shore length1 | Over 50 mi (80 km) |
| Surface elevation | 950 ft (290 m) |
| Islands | Bertrand Island/Halsey Island/Raccoon Island/Liffy Island |
| Settlements | Mount Arlington/Hopatcong/Jefferson/Roxbury Township |
| 1 Shore length is not a well-defined measure. | |
Lake Hopatcong is the largest freshwater body in New Jersey, United States, about 4 square miles (10 km2) in area. Located 30 miles (48 km) from the Delaware River and 40 miles (64 km) from Manhattan, New York City, the lake forms part of the border between Sussex and Morris counties in the state's northern highlands region.
Lake Hopatcong was produced by damming and flooding of two ponds, known as the Great Pond and Little Pond, and the Musconetcong River, its natural outlet. Historically known as a resort lake for vacationing New Yorkers, it is now a mostly suburban residential lake.