So I have discovered the farm, only to realize that it does not produce enough food to sustain my village. How can I get my villagers to fish again? If I put them in the water, they get one fish and then start watering crops. If it's important, I started getting coconuts and farming before algae ever infested the ocean, and it still hasn't yet.

Well, naturally they might water crops instead of fish, but, when the algae does come, this is how to get rid of it SPOILER HIGHLIGHT THE FOLLOWING AREA: Get level 3 farming END SPOILER

Basically, you just have to try different people (or turn the game off where they'll be more likely to fish themselves)