We were camped on Isabella Lake in August 2025. Around 11 at night we saw a glowing something in the water. We watched as it "swam" for about 15 or 20 minutes. The glow was intermittent, irregular lengths of time. Assuming there might be a fish of some kind in the BWCA that glows? Either that or a very big firefly that could swim under water. Not knowing what it was, a member of our group christened it the Spirit of Izzy.

Ok I’m game. Here is my theory.

Somebody was fishing with a lighted slip bobber off shore. Got bit by a fish big enough to break the line and was swimming by your site toting the bobber behind close enough to the surface that you spotted it.

Ya think…

Maybe there was a log floating in the water that had foxfire bioluminescence. Did it dart around like a fish might?

If a floating log had foxfire bioluminescence, you might only see it when the log is spun/rotated to face you, explaining the intermittence.

Or an LED dog toy floating by.

I’m going to guess that you saw is a broken off lighted slip bobber that is hooked onto a walleye.