Lake Hylia is a location in the LoZ. It is the largest lake in Hyrule.
Lake Hylia is where the Zora people are. It is known to harbor a large variety of fresh water fish. It is located in the center of Hyrule, and is also the largest lake there.
Ganondorf is going to use this location as a battlefield to try an get the Zoras to fight on his side. What exactly his plan is is unknown to Hylain intelligence. Both Patrol 1 an 2 were imprisoned in the enemy base here, but the messenger Iris Avis, Cher Ami, saved them by delivering a message to Hyrule Capital.
The final battle in the war is fought here. The Hyrulean Military won even after all of the disorder. The battle was called The Battle of Lake Hylia.