The Pearls of Tessalon are named after a real world medication designed to help people with respiratory ailments cut down or eliminate fluid in their lungs. The drowning sensation of pneumonia sucks and thus this is pretty spot on for naming a water breathing item.
The pearls were a gift from the mermaids of the Bright Shoals to the hero Tessalon for saving them from attacks by the fishermen from nearby villages.
A misunderstanding had grown into outright hatred and the people of the villages were now killing the merfolk they had once partnered with to improve fishing and reduce harm to the reef.
Tessalon had been traveling through the region when his small boat sank. He was rescued by a mermaid and asked what task he might perform as repayment for his life. The mermaid explained the situation and Tessalon pledged to do what he could to make it right.
From village to village Tessalon made his way finding some deed to perform. At Orbach he drove off the raiding goblins. At Highcrest he slew a small dragon that had been stealing children. It was similar at each village and at each the payment he asked was for the elders to meet him on a certain day on a small stoney island just after sunrise.
The elders arrived as promised and once they were all ashore, Tessalon undid the moorings of their small boats and set them adrift. When the elders discovered they were stranded and would surely die of starvation without help, Tessalon shouted from his small boat a solution.
"Make peace with the merfolk and they may be kind enough to recover your boats." Not being complete fools, the elders realized the wisdom of Tessalon's words and before sunset all of the elders had been escorted home aboard their boats.
The merfolk were overjoyed by his success and as a gift of thanks they gave to him the magic pearls that alowed him to breath as they do beneath the surface of the waters.
These small translucent yellow pearls appear to have bubbles suspended within them. Swallowing one allows water breathing for a land dweller over a period of 1d6 + 6 turns.