Glacial Lake Passaic
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Glacial Lake Passaic was 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. The outflow of the lake as it drained formed the gorge of the Great Falls of the Passaic River in Paterson.
The remnants of the lake bed are found in several swamps along the course of the Passaic in central New Jersey, most notably the Great Swamp south of Morristown in northwestern Somerset County.