Lewis and Clark had twice unknowingly passed the mouth of the Willamette River (called Multnomah by them); first while outbound on November 4, 1805, and again on March 30, 1806. However, while encamped opposite the Sandy River Delta on April 2, 1806, Clark learned from two natives of “a large river which discharges itself into the Columbia on it’s South Side Some Miles below us. […] they drew [a sketch] on a Mat with a coal, it appeared that this river which they Call Mult-no’-mah discharged itself behind the Island we call the image Canoe island, and as we had left this Island to the South both in decending & assending the river we had never Seen it. they informed us that it was a large river and runs a Considerable distance to the South between the Mountains. I deturmined to take a Small party and return to this river and examine its Size and Collect as much information of the nativs on it or near its enterance into the Columbia of its extent, the Country which it waters and the nativs who inhabit its banks.” Clark, with six men and a guide, explored about seven miles up the Willamette River. Clark favorably noted, “The Current […] is as jentle as that of the Columbia glides Smoothly with an eavin surface, and appears to be Sufficiently deep for the largest Ship.” He returned to camp on April 3.
The landscape character has altered significantly since 1806 due to riverfront industrialization and channel dredging. However, public access to a more natural setting at the confluence is found at Kelly Point Park, with beachfronts along both rivers, walking paths, and picnic areas.