Steed of the Seas

Stormwrack (Sto)Updated Supplementals (3.5)

Steed of the Seas is a D&D 3.5 spell (Transmutation) from Sto. On class lists for Paladin (Level 2), Paladin Variant (Level 2), Paladin of Freedom (Level 2), and others. Range or area: Touch; Saving throw: None; Duration: 2 hours/level (D); Casting time: 1 standard action.

School
Transmutation
Casting Time
1 standard action
Components
V, S, DF
Range
Touch
Target
The caster's mount
Duration
2 hours/level (D)
Saving Throw
None
Spell Resistance
Yes

Paladins are understandably loathe to enter into the water depths without their loyal steeds to assist them.
With this spell, you imbue your mount with the ability to enter the water without harm by granting it the aquatic subtype.
Additionally, the mount gains a swim speed equal to half its normal speed.
A mount under the effects of this spell is able to breathe water; in fact, it is amphibious and thus subject to no ill effect in or out of the water.