The Columbia Snake River System is a keystone of the Pacific Northwest agricultural economy, an advocate for river users says. An average of 51 million tons of cargo moves through the lower Columbia River each year. About two-thirds of those exports are grain, and about 8.5 million tons of cargo are barged through the inland system of locks and dams, said Heather Stebbings, executive director of Pacific Northwest Waterways Association. The system is the No. 1 wheat export gateway in the U.S., No. 2 in the nation for corn and soybean exports and No. 3 in the world for grain exports, she said.