Many people from Port Renfrew searched all over the San Juan River looking for Foster's old gold site.

Its largest fork begins at a small unnamed pond in Cowichan Valley Regional District and forms the primary headstream.

From here the San Juan River flows southwest into "Pete's Pond" before continuing its descent south.

From here the San Juan River meanders considerably and breaks off into a pair of major branches, forming a large estuary.

The smaller northern branch meanders west before sharing an outlet to Port San Juan with the Gordon River.

The San Juan River Estuary Ecological Reserve was established on 30 April 1996 in order to conserve the alluvial forest communities of the lower San Juan River and protect the red-listed tooth-leaved monkeyflower, endemic to British Columbia.

[4] The estuary is populated by a variety of trees, including red alder, black cottonwood, Sitka spruce, and western hemlock.