When I was the DNR Fisheries Biologist for Sauk and Columbia Cos in the late '60 - early '70s, I did an boomshocker survey on Devil's L. one night. We shocked and captured a Northern pike that was about 40" long. It was in the huge rocks along the west shore.
They were (are) self-sustaining since there was no stocking record for them. I assumed they utilized the small wetland in the southwest corner as a spawning marsh, (now a parking lot?) since that was the only significant inflowing stream.