Bioluminescent beaches are not something you see in many parts of the world, but if you ever do, you’ll remember for the rest of your life. This bioluminescence is cause by an algae called Noctiluca scintillans, also commonly known as the sea sparkle.

https://youtu.be/avS_LmI_-ow

From Wikipedia:

Noctiluca scintillans, commonly known as the sea sparkle, and also published as Noctiluca miliaris, is a free-living, marine-dwelling species of dinoflagellate that exhibits bioluminescence when disturbed (popularly known as mareel). Its bioluminescence is produced throughout the cytoplasm of this single-celled protist, by a luciferin-luciferase reaction in thousands of spherically shaped organelles, called scintillons.

[Via BoingBoing]