Airy Water

You touch a willing creature and transmute the environment within a 20-foot emanation centered on them into a tangible bubble of misty fluid. The creature gains a swim speed equal to their walking speed, and the bubble moves with them and is breathable by both air-breathing and water-breathing creatures. Creatures with a swim speed can move within it normally. Others can walk along or even sit on the bottom of the bubble. They can swim within the sphere at half their walking speed with a successful DC 10 Athletics check. As the bubble is tangible, pushing into or out of the bubble requires a DC 10 Athletics check. If the recipient travels onto land, the bubble must remain in contact with the ground or the spell ends.

Spellcasting within the sphere is unimpeded. Weapon attacks made by creatures within the area against targets within the area do not suffer penalties for attacking underwater. The spell does not filter the air or water, so contamination will continue to have its normal effect - the bubble allows gas exchange freely.

As a Ritual. If you cast this spell as a ritual, its size is reduced to a 5-foot diameter, large enough for a single Medium-sized creature.

Using a Higher-Level Spell Slot. The duration doubles for each spell slot level above 4th.

Adapted from the AD&D 2e PHB spell.