The Coast Guard is investigating the origin of an oil slick reported yesterday afternoon on the Columbia River near Woodland. Around 12:30 yesterday afternoon, a call came in from the four thousand block of Dike Road, reporting a slick about 100 feet off shore. Witnesses say that the slick was about 75 feet wide, and was about a mile upstream from the mouth of the Lewis River. The callers also reported that the slick appeared about a half-hour after a tugboat had gone through the area. It’s speculated that the slick might have been diesel oil. Cowlitz County Emergency Management was notified, along with Washington Emergency Management. The source of the spill hasn’t been determined as of yet.