General chests: you just need to pull the lid.

Chest covered by plants: You need to bring a group of fish to it. You recognise the group of fish because it's shining. It's also never very far.

Clams: they required a certain food, each a different one. The food is the same colour than the clam and it's not very far but rarely close by.

Phytoplanctons (sort of group of fireflies): you need to bring one group to the other, but it can go both ways: bring the yellow ones to the blue ones or the opposite.

Chest with the bottom up: You need the ice beam.

Fish skull: You need to feed something. (It's not that difficult but confusing since you can go inside but receive nothing)

Eells: they need to all be underground more or less at the same time. Some require light other require passing near. (One of them is especially hard because you are without the sub)

Mushrooms (hardly viewable): you need to point the light at tem rapidly.

Chained chest: drops something heavy on it/ use a bomb. (One of them is a bit hard because you need to use a canon with a flashlight to it a stalactite)


Also: Some chest are invisible or sometimes you can't see how to arrive to a treasure: no panic, later you'll receive a sonar that show hidden passages.

When you reach the Garden, explore it a maximum: you can receive an item that can unlocks certains chest.

If you want to add something to this small guide, say it in the comments.