The Collaborative International Dictionary of English v.0.48:

Free-swimming \Free"-swim`ming\, a. (Zool.)
   1. Swimming in the open sea; -- said of certain marine
      animals.
      [1913 Webster]

   2. (Zoology) able to swim about; not attached to a stationary
      object; -- of aquatic animals. [WordNet sense 1]

   Syn: unattached.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

free-swimming
    adj 1: (of animals) able to swim about; not attached [syn:
           free-swimming, unattached]