Silver Scale
From Zelda Wiki, the Zelda encyclopedia
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When you begin the game, Link can only dive under water for a specific amount of time,or depth.(Three seconds or meters) With the Silver Scale, Link's time is extended. To obtain this you must first go to Zora's Domain and talk to the Zora on top of the waterfall, then jump off the ledge into the pool below. You will need to get all of the rupees that he throws down. It costs you 20 rupees to play this mini-game. The reward for when you get up to the top is the Silver Scale:this item enables Link to dive for six seconds.