<P> The Columbia River Estuary is an estuary and a bay on the Oregon--Washington border and the Pacific Coast of the United States . </P> <P> If the Columbia River Estuary is defined by the region that experiences ocean tides, then the estuary extends up the Columbia River to Bonneville Dam and up the Willamette River to Willamette Falls (south of Portland at Oregon City, Oregon). 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 . </P>

What type of estuary is the columbia river