Mushroom Aquatic is inspired by the finding of a species of underwater mushroom. "Until recently, conventional wisdom held that gilled mushrooms did not exist underwater. In 2005, a Psathyrella, a new species was discovered in the clear, flowing, pristine waters of the Rogue River near Crater Lake, Oregon. This discovery opens up a new branch of aquatic mycology, and raises many questions. How many other mushroom species grow underwater?" (Research: Mycellium Running, pg 34, see Coffan, Southworth, and Frank, 2008, in press.)
Mycelium as a medium needs soil microbes to break down and will fully compost in 30 days when broken up into small pieces. It will break down in the water in 180 days. If you leave it outside in a solid shape, it will weather and take a few years to break down. It will last indefinitely indoors in stable conditions.