Hello Marcus

Interesting topic, but I would be really surprised to find that zander have somehow found their way into the Lower Columbia. 

Logistically it would seem a little improbable without a lot of help and concerted effort.

The February issue of In-Fisherman magazine reported

"To our knowledge, no zander exist in North America, except for aquarium species."

In a follow-up article in June-July issue they reported that an article was sent to them by a Nebraska fishery scientist, Daryl Bauer.  It was from the Bismarck Tribune, reporting that an "18.5-inch fish netted from Spiritwood (lake in N. Dakota), had been confirmed by DNA testing to be a zander."

The In-Fisherman article went on to say, "Over one thousand zander were stocked in North Dakota's Spiritwood Lake, (the only known stocking in North America) more than a decade ago; we assumed their demise, based on earlier reports that years of netting by biologists had not produced a fish."

The article went to say that, "the two-year-old status of the fish suggests that natural reproduction had occured," and that the newspaper article went on to quote "North Dakota Fishery Chief Terry Steinwand saying, in effect, that logic suggests that some zander probably remain in Spiritwood, although the population is extremely small give the inability of fishery scientists to catch any of them in test nets."

Now that being said, if an individual were to get in their head to bring in an exotic it CAN be done. 

We have some very large Walleye in the Columbia and it is also possible that someone with a background (caught a zander in their youth etc) was used to catching smaller walleye and then got a big one might have got excited and thought it was a zander. 
The above folks had to use DNA testing to truly establish that the fish was a zander.

Where did you pick up on this rumor?

Anything is possible, but I am very skeptical on this one.

Welcome to the board

BillB