Southgate River, Brook in Pacific Ranges of Coast Mountains, Canada.

The Southgate River is a mountain waterway in British Columbia's Pacific Ranges that travels roughly 65 kilometers through rugged terrain. It originates from Good Hope Mountain and flows toward Bute Inlet, fed by several tributaries including the Bishop River.

The river bears the name of Captain James Johnson Southgate, who settled in Victoria in 1859 and later served in the Legislative Assembly of Vancouver Island. This naming reflects the period of European exploration and settlement in the region during the 1800s.

The river's name honours Captain James Johnson Southgate, a retired ship-master who reached Victoria in 1859 via San Francisco and ran J.J. Southgate & Co., a commission and mercantile business tied to the Royal Navy's Pacific Station at Esquimalt. He sat in the Legislative Assembly of Vancouver Island for Saltspring Island from 1860 to 1863, sold the firm and returned to England in 1865, and died in London in 1894. The Southgate islands, glacier and peak carry the same name.

Access to this mountain river is limited due to its remote and rugged location, and a visit requires careful planning. Visitors should prepare for variable mountain weather and challenging terrain conditions.

A heavy rainfall in 2020 triggered a landslide that created a 100-meter wave traveling 60 kilometers down the valley toward the inlet. This rare event demonstrated the powerful forces at work in this mountain landscape.