Add volumetric underwater god rays to a Three.js scene, marching one drifting swell field along every view ray at half resolution so the light shafts converge on the sun, parallax with the camera and carry rippling caustic streaks, with a shimmering surface underside, a sun that wobbles through the ripples, and the same light dappling fish as they swim through the beams. Use for underwater scenes, oceans seen from below, aquariums, reefs, kelp forests, diving and shipwreck scenes, schools of fish, sunbeams or light shafts through water, caustics, "rays of light shining through the ocean", or watery ripples on a background. Includes a reusable module and the Blue Hour sardine-school demo.