The category for today’s trivial imponderable is “physics.” Do you know . . . the color of water?
Water is actually an extremely faint blue. This color is most visible through the ice of a frozen waterfall. The color can be more strikingly blue when looking “at” the water rather than “through” the water due to the reflection color of the sky. Algae and other microscopic plants can also affect the appearance (or color) of water by reflecting and scattering the light as it returns to the surface.
Source: Sorry, Wrong Answer: Trivia Questions That Even Know-It-Alls Get Wrong, by Dr. Rod L. Evans.