In 1792, Lieutenant William Broughton, a British explorer, led the first trip by non-natives as far up the Columbia River as the mouth of the Sandy River. He and his men camped on Sauvie Island, which lies between the Willamette and Columbia rivers directly opposite the mouth of the slough. Broughton encountered many Chinookans while exploring and mapping geographic features including Hayden Island and other islands in the Columbia just north of the slough. When Lewis and Clark visited the area in 1806, the Clackamas tribe consisted of about 1,800 people living in 11 villages. The explorers estimated that 800 people of the Multnomah tribe of Chinookans lived in five villages on Sauvie Island.