Eighteenmile Island is a 9.89 acre (4 ha) island on the Oregon side of the Columbia River at river mile 174 in Wasco County, Oregon, United States. It is about a half mile (0.8 km) downstream of Mosier, Oregon and four miles (6.4 km) upstream of Hood River. It can be seen from Interstate 84, which runs along the Oregon side of the Columbia River, and from the Historic Columbia River Highway. A small rocky "island" downstream of Eighteenmile Island houses a navigational light.