Clamdust was a reproductive substance produced by great clams. Clamdust clung to individuals who visited a great clam, and would remain on their skin until they found their way to a foreign lake, at which point the clamdust would seed the waters.

In The Lost Barkscrolls, the Great Blueshell Clam of Four Lakes clung to Keris, who washed it off in the lake of the Free Glades. Keris was considered a hero by the Webfoot Goblins for being chosen by an Ancient One and seeding life.