I saw a DIY fish trap that may help (you can google them as well), take a small plastic bottle and cut off the top (about 1/3 down), then invert it and stick it back into the bottle (so the top now points in) then simply put some food (hopefully something that has a favorite scent) into it and leave it in a few hours and check. Don't leave it in too long in case the eel swims in and the water fowls and harms the eel itself. Or drill some small holes in the bottom of the bottle to allow for some water circulation at least and the water does not stagnate. Good luck - what kind of eel is it & how long? I realize that what I described works more for fish but you never know. good luck.