Bio-luminescent plankton. Isn't life wonderful
It's typically not that bright.
Here are some blurry pics I took in Cairns, Australia in some REALLY BRIGHT, stagnant water in the harbor. I had to throw rocks in the water and then snap the pic really quick.
We can get a little bit of it, here. I was at the harbor in Pacific Beach near San Diego last year, and walking in the wet sand would emit a very brief, dim flash in my footprints.