Epidemics, particularly of smallpox and malaria, decimated lower Columbia River Indians after their first contacts with Europeans. The first smallpox epidemic hit about 1775, apparently brought by fur traders in ships. It devastated Northwest coastal villages, including those on the Columbia River. In 1782, another smallpox epidemic, believed to have started in the Great Plains, spread west and reached present-day eastern Washington, where it is blamed for reducing the Spokane Indian population from approximately 1,400 to 700.

Smallpox again ravaged Columbia River tribes in 1801. Lewis and Clark, who traveled west along the Columbia in 1805 and east the following year, described survivors with the telltale pockmarked faces of the disease. Historians believe that by the time the explorers arrived, smallpox had reduced the original Indian population of the mid and lower Columbia River by one-half. Disease again attacked Columbia River tribes in 1824-25 (this time it may have been smallpox) and in 1853.

As lethal as smallpox was, malaria was an even more potent killer. An outbreak at Fort Vancouver in the summer of 1830 lasted four years, raging in the summer and declining in the winter. This single epidemic reduced the lower Columbia Indian population by an estimated 90 percent — in just four years. Malaria is carried by the anopheline mosquito, which was common on the lower Columbia. The disease was known to occur along the Mexican coast, and the epidemic on the Columbia only required an infected person to arrive by ship and get bitten by a mosquito. The disease then spread with terrifying speed. The mosquito’s territory did not extend much beyond Celilo Falls, and so interior Columbia Basin tribes were not affected. The disease did not spread to Puget Sound tribes, either, again because the necessary mosquito species was not present there.

The decimation caused by the epidemic of 1830-33 was so complete that Europeans moving into the area found virtually no Indians. One indication of the slaughter and resulting empty countryside is the fact that Oregon communities were named after others in the eastern United States or were derivatives of family names — Portland, Astoria, Eugene — while many Washington cities, where Indians were more numerous, were given Indian names — Seattle, Tacoma, Spokane, Yakima.