What makes the water in Nil Diya Pokuna look blue?

The striking blue tone of the water in Nil Diya Pokuna happens mainly because of an optical illusion, produced by how cleanly the water reflects the beam from artificial torches onto the pale cave floor.

“Nil Diya” is translated directly as “Blue Water.” Since the pond is protected from direct sun and outside pollutants, the water stays clear, clean, and spotless. When it is lit by strong head torches, the absence of suspended particles lets the light scatter very well, and that is what gives the pool its well-known glowing look.