G’day mate, love your videos. This was filmed on a calm summer night in southern Tasmania. What you are seeing is strong bioluminescence caused by a dinoflagellate species, Noctiluca scintillans. The bioluminescence is triggered by mechanical stress on the cellular membrane, hence the bright flashes as we wade through the water. The biochemistry is fairly complex, but as I understand it, essentially an enzyme called luciferase interacts with the molecule lucifern in the presence of oxygen, emitting a photon. The phenomenon was particularly powerful tonight due to a combination of still conditions, warm water, and an influx of nutrients to the water body from recent rain. I apologise for the hectic audio - my housemates were enjoying themselves. Cheers from Australia