Deep Sea Caillou is a Caillou episode. It is the first episode that Lee-Wun appears in.
Caillou and his friends are at playschool, playing tag and each pretending to be a different type of animal. Just then, a new girl and her mother appear. Caillou greets the new girl and invites her to join in the tag game. However, it seems that she's a bit shy. Inside the classroom, Ms. Martin introduces the new girl as Lee-Wun. She also shows the class something else new. An aquarium that the elementary school donated because they just got a new one. Ms. Martin notes that she herself isn't familiar with all the fish in the aquarium and so she's going to bring in a book about fish. Meanwhile, she says that the fish will need to be fed every day and Caillou is the first to get to do the job. So Caillou feeds the fish, but then it looks to him like the fish are still hungry, so he gives them some more food. He then imagines that he's swimming around in the aquarium. Lee-Wun shows up and tells Caillou that's he's given the fish too much food. She scoops some out, explaining that while the fish may look like they're hungry, it really isn't a good idea to give them too much food. She also has him clean out the algae. She tells him that she has an aquarium at home with snails that feed on the algae. She says that she'll bring some in to help out with the school aquarium. Caillou asks if she ever pretends that she' s in the aquarium and she points out a swordfish and says that sometimes she pretends she's riding on its tail. Ms. Martin notices her talking about the fish and pretty soon, she's telling the entire class about them.