The Lake Of Rage

Gyarados Lake
(The lake is flooded in this pic)
The Lake of Rage (Japanese: いかりのみずうみ Lake of Rage), also known as Gyarados Lake, is a location in Johto. It is located just north of Mahogany Town, connecting it with Route 43, making it the northern-most accessible point of the Johto region. A large lake spans the area of the Lake of Rage, with a few residents living nearby. It is said to be the largest lake in the region. West of the lake lies a labyrinth of trees, which hides a house.
It is said the Lake of Rage was created the last time many Gyarados got together and stirred up a storm. The crater that remained filled with rainwater and became the Lake of Rage. In the middle of the lake dwells a Shiny Gyarados.
To the northwest of the lake, there is a house hidden within a labyrinth of trees. Inside, a man will give Trainers TM10 (Hidden Power) for locating the reclusive house. The path to this house begins in Route 43, on the western side. The house is only reachable when the Lake is flooded.
Southeast of the lake is another house, where a Fishing Guru resides. His greatest dream is to see the world's largest Magikarp, and he regularly measures those brought to him in order to realize it. If the Trainer brings him a large enough Magikarp, he will give the Trainer an Ether as a prize.