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The Water Ring is an underwater object appearing in Super Mario 64 and its remake, Super Mario 64 DS. They are seen only in the ninth course of the game, Dire, Dire Docks. When Mario swims through a Water Ring, it will replenish one wedge of his health meter, and a number will appear above Mario. This number represents the amount of Water Rings Mario has passed through. When Mario swims through five Water Rings, he will be granted with a Power Star.
Water Rings were required for Stars 4 and 5 in Dire, Dire Docks. In Star 4, "Through the Jet Stream", Mario must swim to the other side of the tunnel to find a jet stream spraying out Water Rings. After Mario collects five of these Water Rings, a Power Star appears above the jet stream that Metal Mario can collect. In Star 5, "The Manta Ray's Reward", Mario will find a Manta Ray swimming around underwater and leaving a trail of Water Rings. Mario must follow this trail to collect five Water Rings and make the Power Star appear.