Never heard of a brick built Eel trap, most I have seen are wooden structures in which you placed a wicker basket, however I have heard of brick built wells adjacent to lakes which had a couple of uses mainly as a source of cooking water, folklore has it that these wells when dipped with a water pot often produced an eel and that when that happened water would never boil. Of course that particular tale is nonsense however Eels do cross land to get to a lake or pond and spend a few years there brfore going off to breed. It would be quite easy for an eel to be attracted to a well near a lake and to become trapped within it, my guess is that might be the source of the name.