Silver Scale

The Silver Scale is an item in The Legend of Zelda: Ocarina of Time that allows Link to dive underwater for up to six seconds. It is obtained from a Zora in Zora's Domain if Link collects all five Blue Rupees during the Diving Game.

The Silver Scale is required to retrieve the Letter from Princess Ruto at the bottom of Lake Hylia and subsequently gain access to Jabu-Jabu.

Later in the game, the Silver Scale is replaced with the optional Golden Scale, which further increases the amount of time Link can dive underwater.

Instruction booklet description
"This scale allows you to dive deeper underwater."