Fishermens Friend / Fishermans Foe
Side with the fishermen near Baldur's Gate. / Return Tanya's stolen property.
This quest starts by speaking to Sonner in the area North of Friendly Arm Inn. He will mention a witch affecting fishing. Go to the bridge in to Baldur's Gate and keep walking along the coast to speak to Tenya, the "Evil" Witch, and she will attack. Try not to kill her and you will get another quest to aid her.
Depending on your choice you get the corresponding achievement.