SPOKANE, Wash. (AP) — Environmental groups and the Nez Perce Tribe have filed a lawsuit to prevent dredging of the lower Snake River that enables Lewiston, Idaho, to be the most inland seaport on the West Coast.

The lawsuit, filed Monday in federal court in Seattle, challenges the U.S. Army Corps of Engineers' approval of a $6.7 million dredging project scheduled to begin next month. The lawsuit was filed by Earthjustice on behalf of a coalition of environmental groups. The Army Corps says dredging behind Lower Granite Dam is needed to maintain the barging corridor between Pasco, Wash., and Lewiston, Idaho.

Opponents contend that barge traffic on the lower Snake River is so low that it doesn't justify the dredging. They contend the dredging will hurt salmon, steelhead and Pacific lamprey.