There are two animals in this picture. One in the water on the left and another up on top of some sticks on the right.
Here is a close-up of the animal on the left. If you look closely (click on the image for a larger version) you can see it has a wide, smooth tail which is characteristic of a beaver.
Here is a close-up of the animal on the right.
Here is the animal on the left in a picture taken a second later.
Here is the animal on the right a second later. The pile of sticks, although obscured by some branches in the foreground, appears to be a beaver lodge.
Here is a full frame which was taken at 20x zoom. The other images were cropped from this or a second photograph like it taken a second or two earlier.
After these pictures were taken, the beaver was heard slapping the water with its tail. A few seconds later another slap was heard, possibly by the second beaver.
These photographs were taken a few tens of feet from where a fisher was sighted on February 9, 2010.
Click on an image for a larger version.
Beaver, March 8, 2010
Great Meadows National Wildlife Refuge, Concord, MA
Canon PowerShot SX20 IS