Muskrat in Northern Maine

I got these shots while silently floating in my kayak near a beaver dam
in northern Maine. I watched for about 15 minutes, until the kayak hit
a rock and startled the muskrat. I noticed it would occasionally lift
its tail up in the air, as you see in one of the photos. Was it
pooping? They certainly leave a lot of scat on the shore; maybe they
poop in the water, too.
-Janet