After you release the water you will find a sunken hounfo.
Hounfo is a place of worship and it has a central pillar.
You should do the Nine Tenths of the Lwa spell. It instructs: Establish a veve with sand or chalk in front of the central pillar of a hounfo. Shake an ason over the veve, saluting the four cardinal directions.
You need:
Unlike normal walkthroughs, in Nice Game Hints you can select just the puzzle you want hints for. Here are listed the puzzles for "Connecting the lwa" in Voodoo Detective. The guide you choose only contains information about that puzzle, reducing possible spoilers for other puzzles.