Sounds like you are talking about phosphorescence, a faint blue-green light emitted from the sea at night, either as a continuous glow or a series of tiny flashes. This light is produced by the bioluminescence of living organisms ranging from bacteria to the many species of plankton, including phytoplankton, especially dinoflagellates. On moonless nights in late summer, flashes of light in the surf breaking on sandy beaches are often produced by the appropriately named dinoflagellate Noctiluca. Bioluminescence is produced by a chemical reaction and serves a wide range of functions. Deep in the ocean where there is little or no daylight, almost every species has some light-producing capability. The wavelength of the blue-green light emitted is the same as the residual daylight that penetrates to the greatest depths in the ocean.
Not my own words. Copied from encyclopedia.com. I live on the coast in the UK and see it here from time to time.