Fishing is a great way to make extra money in Harvest World. It can be done off of the dock on the west side of your farm by pressing Space while having your fishing rod selected. Pressing space again will cause your character to reel in the fishing line. If this is done while the water is bubbling around your line, then you will catch a fish. If you reel the line in too early or too late you won't catch anything.
Types of Fish
Minnows are commonly occuring fish that aren't worth very much.
Salmon are less common, but worth $25 to sell.
Bass are somewhat rare, but are worth more at $50.
Tuna are very rare, but are worth a lot at $150.