Need To Know

Why does water turn white?

White water occurs in the upper
course of a river when the
gradient and obstacles disturb
the fl ow of water, causing it to churn and
create bubbles. These bubbles refl ect back
much of the light that hits them, making
the water appear white. Whether a river
fl ows smoothly often depends on its
speed, and the steeper the riverbed, the
faster the water will fl ow.
The combination of fast-fl owing water
and obstacles like rocks causes the fl ow
to become turbulent, with unpredictable
variation in the speed and direction of the

water. This creates a variety of features in
the river. Where water doubles back on
itself, pockets fi lled with bubbles open up;
these provide much less buoyancy and
feel like ‘holes’. Objects lodged in the river
can act as strainers, allowing water to
pass through, but blocking larger debris.
In areas where the water moves rapidly,
it wears away at the surface of rocks
underneath, creating undercuts.
The challenges of navigating the
features of white-water rapids – whether
jutting rocks or whirlpools – attract
kayakers and rafters every year.

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