The deepest lake in the solar system is not located on a planet but on one of Saturn's moons, Titan. The lake is called Kraken Mare, and it is the largest known body of liquid on Titan. Kraken Mare is a hydrocarbon sea, primarily composed of liquid methane and ethane.
Kraken Mare is estimated to be quite deep, with some regions reaching depths of around 300 meters (980 feet) or more. The exact depth and characteristics of Kraken Mare are still being studied, as our knowledge of Titan's surface is primarily based on data gathered by the Cassini spacecraft during its mission to Saturn, which ended in 2017.
It's important to note that within the planets of our solar system, Earth is the only one known to have large bodies of liquid water, such as oceans, lakes, and rivers. Other celestial bodies, like Titan, may have liquids, but they differ in composition due to their unique environmental conditions.