Thanks to Deep-Sea News for the story. Yamba in New South Wales was, for a while, the Cappuccino Coast. According to the Daily Mail:
Scientists explain that the foam is created by impurities in the ocean, such as salts, chemicals, dead plants, decomposed fish and excretions from seaweed.
All are churned up together by powerful currents which cause the water to form bubbles.
These bubbles stick to each other as they are carried below the surface by the current towards the shore.
As a wave starts to form on the surface, the motion of the water causes the bubbles to swirl upwards and, massed together, they become foam.
The foam "surfs" towards shore until the wave "crashes", tossing the foam into the air.
"It's the same effect you get when you whip up a milk shake in a blender," explains a marine expert.
"The more powerful the swirl, the more foam you create on the surface and the lighter it becomes."
Something similar happened 30 years ago, so this is not unique. Tweet