Oregon Coast quandary: Why is the surf brown?

Oregon Coast quandary: Why is the surf brown?
Photo courtesy Tiffany Boothe, Seaside Aquarium

SEASIDE, Ore. -- Why is the surf so ... brown?

Visitors and locals alike have been puzzled by the appearance of the surf, the Seaside Aquarium said.

Some people guessed an oil spill, or water pollution.

The aquarium said the truth is quite opposite: The Seaside area is experiencing a major diatom bloom. Diatom blooms are very healthy and give filter feeders, such as razor clams, a banquet to feast upon, the aquarium said.

Diatoms are single-celled plants (phytoplankton) that are found in both fresh and salt water. They are one of the most important food sources in the ocean, aquarium said.

In the winter, spring, and early summer, diatoms rapidly multiply in the surf zone.  Diatoms absorb large amounts of nitrates and phosphates that are delivered to the ocean by coastal rivers, contributing to their population explosions. 

Everything in the ocean feeds on diatoms and other plankton, either directly or indirectly.  Even the great baleen whales, like the Gray Whale, filter plankton and diatoms as part of their diet.  When the surf zone becomes too saturated with diatoms, they wash ashore.

When they do wash ashore, it is in such great quantities that they resemble an oil spill.

Information and photographs courtesy Tiffany Boothe, Seaside Aquarium