Explore to find the source of water

You explore the strange forest, and you find a beautiful lake.
The water is clean, fresh, and crystalline. A small waterfall hides the entrance of a cave.

You quickly find a few docks, apparently built by local people, but no one is around.
You can explore around the lake or inside the cavern. Maybe you can gather more information or useful objects or supplies that can help you in your quest.