The light blue color in this case comes from air bubbles, not silt. This river isn't sourced in a glacier at all. The light blue stripe below the waterfall is a former lava tube, so it's quite deep in that area. As the water gets agitated where it drops into the crevasse at the waterfall the air bubbles end up getting pushed into the deep water where the current is strong, and they get pulled downstream rather than bubbling to the surface. If you turn around on the bridge this picture was taken from, you can see where the bubble trail eventually works its way to the surface and the light blue color fades out. If it was caused by silt, you'd see the light blue color everywhere in the river, not just in the deep sections, and it would be less blue and more milky on overcast days like depicted in OP's picture.