Big fish in the lake

Am I supposed to do something with the big fish in the lake, or is it there just as a joke? I keep trying to catch it with a fishing lure, but no luck.

You just talk to him by dragging someone onto him and he gives you the task of dredging the lake which gives you one of the tokens

You'll need knowledge level 3 (i think that's the one) before you'll be able to talk to him

He'll want you to clear the lily pads, so you'll need to make the tool for that, too.