I've never seen a muskrat hole go straight down; both beaver and muskrats have the same den characteristics. Muskrats will build houses in shallow swamps, but in every other BOW or river they burrow to make a den.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).