"Swimming Speed +1"
In order to acquire this magical ring, Link must complete the Swimmer's Secret. In a Linked Game of Oracle of Ages, one screen south of Jabu-Jabu's Belly on the surface, Link will encounter Master Diver's Pupil. He is identical in appearance to the Master Diver from Oracle of Seasons. He will give you a Secret and he asks you to tell it to the Master Diver in the Sunken City of Holodrum.
The Master Diver is found inside of the building on the west side of the Sunken City. After completing a short mini-game for the Master Diver, Link will acquire the Seed Ring that becomes the Swimmer's Ring when appraised.
When equipped the Swimmer's Ring will increase Link's speed while swimming. The use of the Swimmer's Ring is very limited in Oracle of Seasons, this is because there are very few areas where Link can swim. It has much more use in Oracle of Ages.