Seaweed is a type of underwater algae found throughout the World of Avatar in places such as the Fire Nation Capital, Republic City, Ba Sing Se, Jang Hui, and the Southern Water Tribe. This underwater organism is consumed as food in the Southern Water Tribe.
While Katara received a palm-reading from Aunt Wu, Makapu Village's famous fortuneteller, Wu made note of her unusually soft palms. Katara told Wu how she used special seaweed lotion that softened her skin; however, an offensive scent was one side-effect.
Later on, Chief Hakoda taught his son, Sokka, how to make tangle mines. He gathered underwater vegetation from the Eastern Sea near Ba Sing Se and used it to fill his mines, along with skunk fish. Intended to be used on Fire Nation warships trying to enter the Earth Kingdom capital, the seaweed in the mines would tangle the ships' propellers and render them dysfunctional. Meanwhile, the repulsive stench of the skunk fish would force the soldiers to abandon their ships.
While invading the Fire Nation Capital during a solar eclipse, Huu used waterbending to gather seaweed and make a giant monster. He controlled the behemoth from the inside with a technique known as plantbending, waterbending the liquid within the seaweed. The monster stayed close to the harbor and protected the submarines from tundra tanks, as they were the only way out of the capital. Eventually, the monster was destroyed by a bomb dropped from an airship. After its destruction, Huu was no longer able to protect the submarines from harm, resulting in their subsequent destruction.
Seaweed is green in coloration and has a high water content. Its texture is soft and smooth. Single strands of seaweed can be quite long, though they vary in size and in thickness.
Huu's seaweed monster was gigantic in size and somewhat humanoid. It had a torso and two arms, but did not have legs or a head; it moved by way of Huu's waterbending. Huu controlled the beast from its core, which had a small wooden mask placed over it as a replacement for a head. The mask was triangular and had two carved-out, pointed eyes.
- Sokka was draped in seaweed after pulling himself out of a river, into which he fell while trying to teach Bosco how to fish.
- The riverbed of the Jang Hui River is filled with seaweed, which often accumulates within clams.
- Sokka used seaweed in conjunction with clams and sand in order to mold a sculpture of Suki.
- Bolin and Korra once dined at Narook's Seaweed Noodlery, where they ate authentic Southern Water Tribe seaweed noodles. At a pro-bending game some time later, Bolin vomited these noodles when an earth disk hit him in the stomach.