- "The Serano Ocean is the largest sea on Sera - stretching across 60% of the planet's surface. But how much do we know of this huge ocean - and how deep does it go?"
- —Settlement 2 Natural History Museum displays
The Serano Ocean was the single largest body of water on Sera, and covered 60% of the planet's surface. In some places, it was at least 6,000 meters deep. Oceanographers divided the Serano Ocean into three depth zones. The Light Zone was the uppermost layer and was evenly penetrated by sunlight; the majority of the ocean's wildlife lived there. Next, at 200 to 1,000 meters deep, was the Twilight Zone, which marked where light penetration declined. Last was the Midnight Zone, which included everything below 1,000 meters and was shrouded in total darkness.
Several sunken cities lay beneath the Serano Ocean's surface. After the destruction of the Hollows in 14 A.E., several Leviathans and Manglers made their way into the ocean. During the Lambent Pandemic, Lambent Leviathans and Lambent Stalks also lurked in these waters.