Seaweed is a type of underwater algae found throughout the world; the waters around the Fire Nation Capital, Republic City, Ba Sing Se, Jang Hui, and the Southern Water Tribe are all sources of the plant. In both the Northern and Southern Water Tribes, seaweed is an important food source, but the tribespeople also use it in a variety of non-culinary ways.
In 296 BG, a servant Kyoshi was tasked with delivering the last jar of pickled spicy kelp of the year to the Avatar mansion. The jar was bent away from her and threatened to be dropped by Aoma, who later tossed it into sky before running away. The jar was saved by Yun, who was falsely identified as the Avatar at the time, and carried into the mansion's kitchen by Kyoshi.
While Katara was receiving a palm-reading from Aunt Wu, Makapu Village's famous fortuneteller, Wu made note of her unusually soft palms. Katara informed the fortuneteller that she used a special seaweed lotion that softened her skin, though it did not have the most pleasant of aromas.
While guarding the mouth of Chameleon Bay, Chief Hakoda taught his son, Sokka, about tangle mines: he gathered seaweed from the Eastern Sea near Ba Sing Se and put it, along with skunk fish, into a container made of animal hide stretched over a bamboo frame. 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, with the repulsive stench of the skunk fish forcing the soldiers to abandon their ships.
During the invasion of the Fire Nation on the Day of Black Sun, Huu used waterbending to gather seaweed and create a giant, humanoid mass. He controlled the behemoth from the inside with a technique known as plantbending, waterbending the liquid within the seaweed. Huu stayed close to the harbor and protected the invasion force's submarines from attack, as they were the invaders' only way out of the capital. The monster was eventually destroyed by a bomb dropped from a Fire Nation airship, leaving Huu unable to protect the submarines from harm and resulting in their subsequent destruction.
Aloe lotion infused with seaweed is a component of the "tea-leaf skin wrap", an elaborate spa treatment offered in Republic City. The treatment was a favorite of Prince Wu's, and he recommended it to Buttercup Raiko.
Seaweed is green in coloration and has a high water content. Both soft and smooth in texture, single strands of seaweed can be long, though they vary in size and 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. Huu controlled the beast using waterbending 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.
- The Water Tribes also use seaweed to make bread, sprinkles, and cookies.
- 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, along with shells and sand, to mold a rather grotesque sculpture of Suki.
- Narook's Seaweed Noodlery is a popular restaurant in the Little Water Tribe neighborhood of Republic City. Bolin and Korra once dined here, where they ate authentic Southern Water Tribe seaweed noodles. At a pro-bending match some time later, Bolin vomited these noodles when an earth disk hit him in the stomach.
- Seaweed soup is a remedy for blood loss.