Electric fish barriers generate really strong fields, using buildings' full of power electronics. They are surrounded by fences with prominent warning signs, and if you fall into the water I'm pretty sure you die.

So maybe something like this could be "switched on" temporarily -- run on batteries for a few minutes -- but you sure wouldn't want the boat to run with this on all the time. It probably wouldn't even be possible, energetically.

But yeah, electric eels do exist.

Maybe a big drum of capsaicin would be better.

Ideally you'd find a way to befriend them though. Some kind of carrot instead. Hm.