Protodermis Sea

The Protodermis Sea was the seemingly endless ocean in which Metru Nui floats.

History
The Toa Metru crossed it when saving the Matoran from Makuta. During Makuta's battle with Toa Vakama; the Kanohi Vahi, the Mask of Time was knocked into this sea which exposed and changed the Kanohi's color to rusted orange. Some time later, Vakama managed to retrieved the Vahi.

It was crossed again when the Toa Metru were returning for the rest of the Matoran. It was later crossed by the Toa Nuva when they were returning to Metru Nui in their quest to awaken Mata Nui.

During or around the time of the Great Rescue; The Shadowed One tossed a Kanohi Kakama (which had belonged to a Toa Mangai killed by Dark Hunter, Eliminator) into the sea.

Much later, Piraka Reidak and the other five Piraka decided to raid Mangaia and discovered the crushed armor once belonged to Makuta Teridax. Reidak attempted to claim the Kanohi Kraahkan, however the Kanohi defended itself by shooting Shadow energy at him. Enraged, Reidak quickly threw it to the sea. The Kraahkan was later retrieved and briefly worn by Makuta Icarax.

Destiny War
A part of the sea near Metru Nui was occupied by a Brotherhood of Makuta battleship with the Makuta army hoping to besiege the city. However, the battleship was destroyed and the army were all killed by a fierce storm caused by Mata Nui's awaking.