Glacial Lake Passaic was a prehistoric proglacial lake that existed in northern New Jersey in the United States at the end of the last ice age approximately 13,000 years ago.

The lake was formed on the western side of the Watchung Mountains by a blockage of the Passaic River from a moraine left by the retreat of the glacier. The river had previously passed through the Watchungs near present-day Summit. After the raising of the lake's level, the river found a new temporary course to the sea near present-day Bernardsville. Eventually the river formed its present course, a circuitous detour around the north end of the Watchungs through present-day Paterson. As the glacier retreated, the lake found a new outflow to the ocean via Great Notch near Totowa and Upper Montclair, which eventually drained most of the once mighty lake, leaving smaller lakes that eventually dried up. As the glacier retreated further to the north, the outflow of the lake drained towards the north and formed the gorge of the Great Falls of the Passaic River in Paterson.

The remnants of the Glacial Lake Passaic lake bed are found in several swamps along the course of the Passaic River in northern New Jersey, most notably the Great Swamp south of Morristown in northwestern Somerset County and extreme southern Morris County. Higher elevations in these areas, such as Long Hill Township and parts of Madison, formed islands within the massive glacial lake.

See also

*Depiction of Lake Passaic as it Existed 11,000 to 13,000 years ago.
*List of prehistoric lakes

Passaic
Category:Geography of New Jersey