It could have been green sturgeon, depending on how long ago it was, but if it was in the last 15 years or so, it was almost definitely white sturgeon. Greenies are critically endangered worldwide, and the Columbia is one of the last strongholds for them.
Sturgeon are a major foodfish the world over. In Europe the Lake and Beluga sturgeon are prized game and table fish. Also, almost all high quality caviar is sturgeon roe (although in the Southeast, poachers often substitute paddlefish roe).
Sturgeon farms were big business in the early 20th century. My native Klamath Basin did not have native sturgeon, but there was a sturgeon farm near the lake about 100 years ago. During a particularly bad storm, the wooden fish screens were broken, allowing the fish to escape to the lake and establish a population.
Today, they are few and far between in the Basin, but I did see one once while fishing the crystal-clear waters of the Crystal Creek arm near Rocky Point. It was only 3-4 feet long, but it made my week. About 5? years ago, the local newspaper ran an article of a 10+ footer that was pulled out of a drainage ditch after getting caught in a fish screen. It completely filled up the back of the extended bed pickup and still hung over the side...
If you catch a keeper in the Columbia or elsewhere, feel free to keep it, but keep in mind that female white sturgeon don't reach sexual maturity until they are at least 20 years old, so breeding is very slow...
