Fire Nation Army factory

A Fire Nation Army Factory is located at the shore of the Jang Hui River; this smelting plant is where the Fire Nation army makes metals for various weapons and vehicles. The cooling system provided by the river water helps in the production of a tough, new metal for armor. However, as a result, the plant dumps a significant amount of waste into the river while large smoke stacks simultaneously contaminate the air. To General Mung, this pollution is a small price to pay for building weapons that can help win the war.

History
The factory was built years prior to the start of the show and it quickly affected surrounding ecosystems. It was the excessive pollution from this plant that led to the plight of the Jang Hui fishing village, where most of the population was sickened by the water and left to starve from the lack of healthy fish.

The factory was destroyed by Aang and Katara in "The Painted Lady", during which Katara masqueraded as the Painted Lady, the spirit who protected Jang Hui. General Mung responded by sending a team of domestic soldiers to destroy the defenseless village. They were driven away by Katara and Aang, who warned them never to return. The loss of this sinister factory has allowed Jang Hui to thrive once again.

Trivia

 * The factory is one of the more advanced buildings in the show.