Waverider BardingEquipment 5
Source Pathfinder Lost Omens: The Grand Bazaar
Price 130 gp
Weight light
This light barding is covered in wavelike patterns. The barding adjusts to fit your animal companion regardless of its shape.
Activate 
Interact
Frequency once per day
Effect You trace a finger along the wave patterns on the barding, granting your companion a swim Speed of 30 feet for 10 minutes. If your companion already had a swim Speed, it gains a +10-foot item bonus to its swim Speed for 10 minutes instead. Even if the companion doesn't have the mount special ability, it can still Swim while being ridden.
Traits
Something of uncommon rarity requires special training or comes from a particular culture or part of the world. Some character choices give access to uncommon options, and the GM can choose to allow access for anyone. Less is known about uncommon creatures than common creatures. They typically can't be summoned. The DC of Recall Knowledge checks related to these creature is increased by 2.
CompanionAn item with this trait can be worn by an animal companion or similar creature. A companion can have up to two items invested.
InvestedA character can wear only 10 magical items that have the invested trait. None of the magical effects of the item apply if the character hasn't invested it, nor can it be activated, though the character still gains any normal benefits from wearing the physical item (like a hat keeping rain off their head).
PrimalThis magic comes from the primal tradition, connecting to the natural world and instinct. Anything with this trait is magical.
TransmutationEffects and magic items with this trait are associated with the transmutation school of magic, typically changing something's form.