(AP) Two Pacific Northwest tribes are demanding the removal of three major hydroelectric dams on the Columbia River. The Lummi and Yakama nations said Monday that the U.S. government was in violation of a treaty from 1855 when it built the concrete dams on the lower Columbia River, destroying important native fishing sites and the migration of salmon. The three dams are a critical part of a complex hydroelectric network in Oregon, Washington and Idaho that powers the region.