got call about beaver pond yesterday ,so met guy today an we walk out to pond ,big pond two house ,5-7 inches of ice ,where there is not a bubble trail ,2-3 inches of ice in bubble trail ,

and then this , a hole an tunnel that goes under ground too pond , water in hole is not frozen , anyone ever seen this

Trapped a steep sided field ditch where the beavers had dug tunnels into the woods and out into the corn field. Sure does make it intetesting walking to check sets. You would be walking along and then there would be a hole 12 inches or so across and one leg would go in to your hip and not find bottom. Dont ask me how i found out.

Had the same thing happen at a couple places and your right it makes for an interesting experience

Also seen it several times late in the year before ice out, I think the beaver just want to get out and get some fresh food

why would water not be frozen in earth hole other than beaver coming an going , ground warmer ???

The dirt is warmer than the air, thus allowing the water to not freeze.... I dont know

See it often around here in the black muck ground.
water under ground is warmer.

I trapped a couple places last year that were identical to your situation. They had passage ways burrowed all over the place....even in 20F degree weather you had to be careful where you walked otherwise you ended up with a wet leg as some of the tunnels only had a roof of 2-3 inches of dirt. I doubt these beaver ever got frozen in provided they used the access holes daily.

Spring?

That spot is getting more sun, like in the picture, the peat is staying warm, and working as an insulator. Find a spot like that occasionally where an ash tree has fallen over in the bog and the root system gets full sunshine. Beaver make feed beds under them often. I found a big hummock once out in the center of a bog. The otter had sratched the top off and using it for a toilet at one time, so exposed all the dark peat. Sun kept it warm and when I first saw it I thought it was a smaller beaver feeder house. My chisel would just drop right through the top and there was a platform inside the rats and beaver were using. I trapped that pond for about two weeks and it eventually even formed a chimney.

I find those holes in places beaver have eaten all the close food and have tiny feed beds. My guess is a back door to the grocery store. I will add in ever situation the location has had beavers for a very long time

I had this same deal once,except i set the entrance under the ice.In about a month i took 3 otters out of that one conibear.I always figured it was an warm spring flowing underneath that caused this,on extremely cold days the snow around the openings would be crystallized.

We get those tunnels as well with our bank den beaver and our water never gets hard.

Interesting to say the least!