The region containing a legendary leviathan's lair is warped by the leviathan's magic, which creates one or more of the following effects:
- Water levels are raised by 30 feet within 6 miles of the leviathan's lair.
- Sea creatures are aggressive towards non-sea-faring creatures within 1 mile.
- Trenches within 1 mile of the leviathan's lair form portals to the Elemental Plane of Water, allowing creatures of elemental water into the world to dwell nearby.

If the leviathan dies, these effects fade over the course of 1d10 days.