Defile Water

You touch an area of water that fits within a 60-foot cube, defiling it for the duration. The water sours with scum and produces an acrid odor. When a creature enters the defiled water for the first time on a turn or starts its turn there, it must make a Constitution saving throw. On a failed save, a creature takes 4d6 poison damage and is poisoned. On a successful save, a creature takes half as much damage with no additional effects.

When a creature poisoned by this spell starts its turn outside of the defiled water, it can make a Constitution saving throw. On a success, the creature is no longer poisoned.