>>11363939Looks like caustics to me. When light shines through tiny ripples in the water, the nonuniformity causes refracted light to bunch together, tangent to curved surfaces which you see as the bright lines. You see the same effect in a swimming pool on a bright day.
Interestingly, a three-dimensional version of the effect, applied to small density variations in the early universe, explains the filament and void structure of the universe:
https://www.youtube.com/watch?v=UmHQ2Y1hD0U 
