I have caught freshwater eels in several different landlocked ponds in NC and Virginia, usually catfishing at night. Don't know how they got there but with the several different locations that I have caught them would not believe that they were all stocked, especially since this is not standard American tablefare. All literature that I have seen on them though has said that the are migratory from the ocean. The ones caught in NC were in coastal counties but the eels caught in VA were far inland. Though this doesn't answer your question Watergirl thought I would pass on an observation.

Don