Young otters are usually with the whole family. If the tail was like a rat tail - i.e. hairless, then it was a muskrat. If the tail was furred, and the animal was relatively long and slender, I'm betting on a Mink.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).