The Columbia River Estuary is an estuary and a bay on the Oregon-Washington border and the Pacific Coast of the United States.
If the Columbia River Estuary is defined by the region that experiences ocean tides, then the estuary actually extends up the Columbia River to the Bonneville Dam, and up the Willamette River to the Willamette Falls (south of Portland). If the estuary is defined by the geographic land form or by the inland extent of salinity, then the estuary extends only as far as Welch Island.
It is the mouth of the Columbia River. Settlements on the estuary include Astoria and Warrenton in Oregon.