I noted the previous advice about small low ponds and made several 3 X 3 ponds but no luck. So I started trying to deepen one of them and it ended up all different levels. An electric eel appeared in a section that was only one square wide, but it didn't bite before my time ran out for the day. The next day I went back, another eel appeared quite quickly and I caught it .
It was summer, about 8.30pm and the elevation was HE minus 16 (that is, 16 levels lower than the house). The eel makes a big shadow like an arapaima and takes about the same effort to catch.
Tip for making a deep lake more easily:
Dig a hole maybe 3 X 3 to right depth fairly close to a water source, allowing for escape stairs of course!
Cut a channel to let the water in. If a little fence appears then fill the space in front of it. Then when you dig the same square again it should fill with water. You might have to do this every step of the way, which is why extra width is useful at this stage to manoeuvre.. When the water has flowed to the depth you want then block the channel and make the pond narrower but keep it long as the eel is big.
Wish I'd done it this way around first time - duh!
Rob