In the Forgotten Realms, Umberlee is the vengeful and sadistic goddess of storms and the ocean. Players can visit one of her temples in Baldur's Gate 3 by heading south from the Gray Harbor waypoint, and when the party shows up they're mourning the loss of one of their sisters.
Baldur's Gate 3: How To Complete Avenge the Drowned
This quest can be simple to complete, but players must be very careful about when they get and complete it.