Muskrat or beaver?

Directly behind my townhouse is a large detention pond (filled with dormant reeds), and abutting that, on the property of Singing Hills Forest Preserve, there is a natural depression which becomes a lake during wet periods as seen below.


Several times last week, I saw a dark shape swimming in an open area amongst the reeds, and today it was perched on a mud/foliage mound eating reed stalks. Despite binoculars and a 300mm lens on my digital SLR Nikon, I can't tell if it is a beaver or a muskrat, since I haven't gotten a clear view of its tail to see if it is either a long snake-like tail or a floppy paddle-like tail. Anyone have an idea from this photo? (Click photo to enlarge.)




It's a muskrat -- see here.