Merggles are a race of aquatic Fraggles who live among the roots and limbs of the Great Tree in the Fraggle Rock episode "Beyond the Pond". Merggles are the Fraggle version of merfolk — the lower half of a Merggle's body is akin to a fish's tail.
When the Great Tree starts to weaken, Red confesses to the Merggles that she poisoned its roots. Mortified, the Merggles commit to journeying to a far-off lake, and lock Red away in a cage. Mervin is the last to leave, whom Red convinces to move her closer to the tree in order to communicate with her friends, in exchange for the purchase of two hats. When Gobo arrives, he confirms that the Fraggles stopped poisoning the roots, and the Merggles let Red go. Later, the Merggles visit Fraggle Rock in time for the underwater frolic.