Not really my usual area (I'm more of an NDE nerd tbh) but this caught my eye and I can't just scroll past without saying something.
A creek in Norway where I live would have me thinking giant pike before anything else - those things get absolutely massive and move in ways that mess with your head at night. Could be something similar depending on where you are?
That said, ". Definitely not a beaver". Is doing a lot of heavy lifting here. How confident are you actually? Because people consistently underestimate how large beavers look when they're partially submerged and moving fast. The water distorts everything.
But - if you genuinely ruled that out, a few questions worth thinking about:
How long would you say it was, roughly?, Was it moving through the water or sort of on top of it?, Any sounds?
The creek location is interesting too. Out-of-place animals often follow waterways, so if there's been any sightings upstream or downstream that would be worth checking local news for.
I'd also say - grab a trail cam if you haven't already. Doesn't need to be anything fancy, a basic Blink or Reolink unit pointed at the bank would at least give you something concrete. Eyewitness accounts alone tend to go nowhere fast on here, as I'm sure you've noticed.
What's the general region? That would help narrow down what's actually plausible versus what's wishful thinking.