Befriending the Water Element

From: Martha
Description: The messenger crab brought word from the emperor: He has sent me the artifact I need, and the river will bring it to me. Look, there is a coffret on the riverbank! There was nothing there a moment ago! Could you use your artifacts to open it? This coffret is securely sealed.
Completed: I can’t believe my eyes! This is it - the artifact that makes the water element more friendly to the City of Shadows. After all, if it’s not one mess, it’s another: one day it’s raining buckets, the next day the rivers start flowing backwards... I’ll see if I can figure out how this thing works.