Clarity Lake

Clarity Lake is an -exclusive location in Johto, which was featured in Mewtwo Returns.

It is the source of Purity River. It was originally located in the center of the forest atop Mount Quena, but was moved to inside the mountain by after it defeated Team Rocket.

Due to the extreme weather and steep mountain face required to overcome in order to access the lake, it is left pure and undisturbed by humans. This purity makes the lakewater especially pure, giving it healing properties.

Because of its properties as well as it being a breeding ground, the Pokémon view it as sacred, and will attack anyone who threatens its stability. The local Pokémon drink from the water regularly, making them healthy despite the lack of s.

An island is located at the center of the lake. After the events of Mewtwo Strikes Back, the clone Pokémon have made this island their home. Despite the lake being said to be undisturbed by humans, the island contains a prison cell inside a cave.

History
After and the Team Rocket Combat Unit capture  on top of Mount Quena, they begin work on a new secret base (a laboratory in the English dub) there. In the process of construction, they begin pumping pollution into the pure lake.

When Mewtwo was injured due to Team Rocket's machine, threw it into the lake in order to revive it. Once Mewtwo was restored, it destroyed Team Rocket's aircraft, then moved the lake to inside of the mountain to keep it secret, taking the clone Pokémon, Ash and his friends inside the mountain with it. Mewtwo swore Ash and his friends to secrecy so that the lake would remain undisturbed, but allowed them to keep their memories.

In other languages
Lago della Chiarezza