From Zelda Wiki, the Zelda encyclopedia
A Whirlpool Waterway in A Link to the Past is a magical form of transportation (or form of warping) that exists in the bodies of water in the Light World and Dark World. As the name suggests, it is a whirlpool that transports Link from one body of water to another. According to King Zora, it is the waterway used by the sea folk. It resembles the whirlpools seen just before River Zoras surface to attack Link, but unlike the whirlpools created by the River Zoras, they do not disappear. There are six of them in the Light World and two of them in the Dark World. Whirlpool Waterways work in pairs, meaning that when Link takes one to another, he can go back to the location he warped from by swimming back into the destination whirlpool. Each whirlpool will always take Link to the same preset destination. There are two whirlpools in Lake Hylia, one in Zora's Lake, one in the pond between the Sanctuary and the Fortune Teller north of Kakariko Village, one close to the Witch's Hut in Zora's River, one in the Great Swamp, one in the Dark World River (close to the Dark World equivalent of the Witch's Hut), and one in the Dark World equivalent of Lake Hylia. The six Whirlpool Waterways can only be used after Link obtains Zora's Flippers.
The Whirlpool Waterway in the Dark World equivalent of Lake Hylia in A Link to the Past