The ocean is very, very deep; light can only penetrate so far below the surface of the ocean.
The ocean is divided into three zones based on depth and light level. The upper 200 meters of the ocean is called the euphotic, or "sunlight," zone.
Only a small amount of light penetrates beyond this depth.
The zone between 200 meters and 1,000 meters is usually referred to as the "twilight" zone, but is officially the dysphotic zone. In this zone, the intensity of light rapidly dissipates as depth increases.
The aphotic zone exists in depths below 1,000 meters. Sunlight does not penetrate to these depths and the zone is bathed in darkness.
In which Sasha Calista Laurier is tasked with baby-sitting the only boy who manages to push her buttons, putting her in the middle of all of Olympus's bullshit.
Oh, and did I mention this boy could be the most powerful demigod of their generation?
PERCY JACKSON X FEM OC FANFIC
TLT - TTC (eventually)