Turtle?

raccoon? Was anything else messed up, overturned?
How deep is your pond? Do you have a shelf?

could be a muskrat if you have them around there. They made a real mess out of my client's pond. She thought they ate all the water lilies, but it turns out they are messy eaters. The small pieces of the roots floated around and are coming up all over the edges of the pond now.

Deer, Squirrel, Raccoon maybe!