Seaweed

A seaweed is a type of underwater plant found sporadically in the World of Avatar. It is edible and grows in the waters near the Fire Nation Capitol, Republic City, Ba Sing Se, and Southern Water Tribe, among other places. This underwater organism has found a prominent place in many cultures, as it has become a popular cuisine in some societies, including the Southern Water Tribe.

History
Seaweed was first mentioned when Chief Hakoda taught his son, Sokka, how to make tangle mines. He gathered underwater vegetation from a lake near Ba Sing Se and put it all into his mines, along with skunkfish. Intended to be used on Fire Nation warships trying to enter the Earth Kingdom capitol, the seaweed in the mines would tangle the ships' propellers and render them dysfunctional. Meanwhile, the repulsive stench of the skunkfish would force the soldiers to leave their ships.

When attacking the Fire Nation Capitol during a solar eclipse, Huu used waterbending to gather seaweed and make a giant monster. He controlled the behemoth from it's inside via waterbending the liquid within it, a technique known as plantbending. The monster stayed close to the harbor and protected the submarines from tundra tanks, as they were the only way out of the capitol. Eventually, the monster was destroyed by a bomb that fell down from an airship. After it's destruction, Huu was no longer able to protect the submarines from harm, so they were subsequently destroyed. There is little seaweed in the Fire Nation, so it took him a while to collect enough for the monster.

Seventy years later, Bolin and Avatar Korra went on a date, during which they visited an authentic Southern Water Tribe cuisine restaurant in Republic City - Narook's Seaweed Noodlery. Here, they ate seaweed noodles for dinner. It was Bolin's favorite restaurant, and Korra noted that the noodles were very tasty and undeniably authentic. At a Pro-Bending game a few days later, Bolin barfed out these noodles because a projectile hit his stomach.

Description
Seaweed is always green and filled with water. The texture is soft and smooth. Single strands of seaweed can be quite long, though they often vary in size. Seaweed can also be of many different thicknesses. The seaweed that is found in noodles tend to be shorter in length but thicker.

Seaweed monster
Huu's seaweed monster is gigantic in size and somewhat humanoid. It has a torso and two arms but does not have legs or a head; it moves by way of Huu's waterbending. Huu controls the beast from it's core, which has a small wooden mask placed over it as a replacement for a head. The mask is triangular and has two carved-out and pointed eyes.

Trivia

 * All times seaweed has appeared or been mentioned in the span of the two series, it has been at or in the vicinity of a capitol city.