How do you find a Mermaid or Merman?

I saw a merman and that evil mermaid once as my sim was swimming around near her house (unfortunately a mod cause my game to crash and I hadn't seen them since). Yes, your sim can get kelp. Go to rewards and use points to buy one. They are around 500 points. You might find kelp around as well.

I think you can find kelp by exploring the caves.

there is mermaid kelp in the cave, turns you into a mermaid or merman