Sometimes the foam on the beach is brown which may lead us to think there’s pollution around.
A Horizons Regional Council PDF explains though that it isn’t pollution but an algal growth:
The brown foam seen on our beaches from time to time is surf algae, also known locally as surf scum.
Surf algae are always present in the surf-zone but sometimes there is a population explosion. This is when large amounts of unsightly brown foam makes a nuisance of itself in the surf and on the beach.
It can easily be mistaken for some kind of pollution event, but it isn’t.…
Surf algae are simple, microscopic plants. They just need nutrients and sunlight to grow. They attach to bubbles in the surf so they float near the surface where there is plenty of sunlight for growth. The brown foam is a collection of millions of these algae filled bubbles.…
Surf algae identified from west coast beaches are not known to produce toxins. In fact there is research saying that surf algae are a source of food for shellfish such as tuatua and toheroa.…
Surf algae blooms are caused by a combination of many things in the surf-zone environment. One of these is likely to be nutrients from major river inputs along the west coast.
Read Brown foam on the beach (500 KB PDF) for the whole story. It’s only a single page.
