I guess you mean the lake with the corrupt water...
If it's about the potions:
Explore until that something does not happen. If your character is fast enough you can escape from fights or use the bomb which is usually successful with most enemies.
If it's about the way:
Your player character needs a source of light. There are at least three items that do shed light. One of these can be made if you char has built a special room in the teachers hut, one will be given as a gift (depends on your choice in a quest) and one can be bought.
Tell me if you want me to be more explicit.