I spied this amongst the cattails in the pond and cannot say for sure whether it is a lodge or just a "push-up". The latter is formed when muskrats push up plant matter (usually cattails) through a hole in the ice and often use them as feeding platforms. This one is too dilapidated and I can't see if there is a hole in the top, so, I'll just say it is a sign of the muskrats in the pond.