The dam provides for slackwater navigation, hydroelectric power generation, recreation, wildlife habitat, and incidental irrigation.

[4] The United States House of Representatives rivers and harbors committee initially approved the project in April 1941; navigation, power generation, and national security were the major reasons cited for construction of the dam.

The Washington side also has an 86-foot (26 m) wide, 683 foot (208 m) long navigation lock that lifts boats an average of 75 feet (23 m).

In the event of a large-scale grid outage, McNary would provide the black start capability necessary to restart other generation facilities.

The dam is equipped with three large "fishway" pumps which provide water to supplement the mostly gravity-fed fish ladders.