PORTLAND, Ore. (AP) — A critical boat lock on the Columbia River has shut down for repairs, meaning barges that shuttle millions of tons of wheat, wood and other inland goods to the Pacific Ocean for transport to Asia can’t move.

Chris Gaylord, a U.S. Army Corps of Engineers spokesman, said Monday a crack in the Bonneville Dam lock’s concrete sill was discovered late last week. It’s not clear when repairs will be complete.

The closure comes during wheat harvest and will be devastating for farmers who ship their grain to Asia if it drags on.

The Bonneville Dam is the first in a series of eight dams on the Columbia and Snake Rivers, which together make up a watery highway for goods flowing into and out of the region from the Pacific Rim.