The East and West Lakes are two large bodies of water located in the central Earth Kingdom, to the southwest of Ba Sing Se. They are divided by the pinnacles of rock that form the Serpent's Pass, and connected only by a small gap in the middle of the pass. Both lakes are connected by rivers to the sea, with the West Lake connecting to the Mo Ce Sea and arctic seas, and the East Lake to the Eastern Sea.
Prior to AvatarAang's return, the Fire Nation seized control of the West Lake from the Earth Kingdom, and sent ships to patrol along the Serpent's Pass and scan for intruders. Rumors spread that the Fire Nation was working on a secret project in the West Lake and did not want anyone investigating. The East Lake, however, remained under Earth Kingdom control, with one of its harbors, Full Moon Bay, serving as the main transfer point for refugees headed to Ba Sing Se.
However, after the Earth King was overthrown, the Fire Nation, under the command of AdmiralLiang, quickly swarmed into the East Lake, forcing the Water Tribeforces, along with Aang and his friends, to abandon their defense of a nearby bay. After scuttling the Water Tribe fleet in the center of the East Lake and commandeering a Fire Nation patrol vessel, they fled west, and later approached a barrier constructed by the Fire Nation to control traffic through the gap in the Serpent's Pass. Hakoda and Sokka managed to convince the barrier guards to let the ship into the Western Lake, only to run into a patrol ship from the Western Fleet. After mistakenly revealing themselves to the ship's commander by commenting on having received orders from Admiral Chan, who was, in reality, on leave, they engaged in a skirmish with the ship. However, the group managed to escape with relatively little damage.