Lake Hopatcong, New Jersey

Lake Hopatcong
at sunset seen from Bertrand Island
Location	Morris / Sussex counties, New Jersey, United States
Coordinates	40°57′N 74°38′W / 40.950°N 74.633°W / 40.950; -74.633Coordinates: 40°57′N 74°38′W / 40.950°N 74.633°W / 40.950; -74.633
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 Township, New Jersey/Roxbury Township, New Jersey
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 from the Delaware River and 40 miles from 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.

The exact origin of the name Hopatcong is unknown, though it is most commonly attributed to the Lenape Indian word for "stone water," or "stone over water". Some linguists believe "Hopatcong" to be a derivative of the Lenape word hapakonoesson, meaning "pipe stone". One explanation of the origin of the word Hopatcong is that it was a derivation from the Lenni Lenape word Huppakong meaning "honey waters of many coves", but this wording was probably invented at the beginning of the 20th century to stimulate tourism.

Before the late 1700s, Lake Hopatcong was known by several names, including Great Pond and Little Pond (before flooding into a single lake), Sandhay Sea (circa 1648), Brookland Pond (mid-1700s), and Musconetcong Pond (1769).

Before the last ice age, the waters of the prehistoric Hopatcong basin fed into the Raritan River. The glacier that shaped much of the New Jersey Highlands formed a long terminal moraine that forced water from the basin into the Musconetcong River. The glacier left behind two ponds, nearly two miles apart.

In the early 1700s, the Great Pond stretched between Henderson Bay and today's Hopatcong State Park. Little Pond was a small body of water to the south of Woodport. The two lakes were first dammed in 1750. By 1831, Lake Hopatcong had been flooded to nearly its current shape.