The Merman Chamber is a large circular room that has a big trident symbol on the floor, with 12 curved bioluminescent pillars surrounding it, and a stand with mysterious symbols on it. The roof above the trident symbol opens up every full moon to project the moonlight straight in from the night sky. It was built by mermen centuries ago, during the war against mermaids for ownership of Mako Island. Just like the Trident Cave, the rock entrance to the cave only opens during a Full Moon or when exposed to full moonlight.
It was designed to destroy all mermaids across the world by combining the trident and the full moon to absorb power from the Moon Pool and subsequently every mermaid's life. The merman who built the chamber fell in love with a mermaid and decided not to activate it, and instead found ways to invoke peace and stop the war once and for all. Since only a member of that merman's bloodline could activate the chamber, no other merman had been able to use it since then, and it became a lost ruin.
Thousands of years later, the chamber was discovered by descendant Zac Blakely when Ondina and Mimmi wanted to test his reaction to the moonlight. Zac and Mimmi saw the cave in a vision and traveled to Mako Island to look for it. Zac found it by feeling it's location. They opened the hidden entrance with Sirena's Moon Ring. Once Zac went near the stand and placed his hand over it, the symbols started to glow. Ondina tried to stop Zac, but was teleported out of the room into water somewhere. The next three full moons, Zac went to the chamber to activate its power but was interrupted every time.
Another merman named Erik wanted to release its full potential, believing it could add to the power between mermen and mermaids, and used the trident's rock to steal Zac's power when he refused to do it. By releasing the chamber's power, mermaids almost died until Zac stopped it although he nearly dies himself in the process. The trident stone is then turned to dust after Mimmi uses it to heal Zac, thus ending the chamber's threat permanently.
Five symbols surrounding Mako Island needed to be activated beforehand, then a code must be placed in order. The sequence is the following: The rising moon, the volcano, the full moon, the Moon Pool and the trident.
Once the code is put in, the trident symbol in the center will project a hologram of the trident. The weapon itself or the stone was to be placed in that hologram, which will then transfer the water from the Moon Pool into the trident symbol and form a pillar of water, while slowly draining the life forces of mermaids. To stop the process, the stone needs to be removed.
No mermaid can walk on the trident symbol in the chamber. If one were to step on it, they will be transferred to an unknown location, unable to be found unless Zac uses the pedestal to bring her back.
- The Chamber's magic was ineffective against transformed mermaids, evident by Evie McLaren's immunity when it activated, indicating that Evie is a "half-mermaid." This is due to the fact that she was born as a human.