Marine algae & plankton

What's that in the water? A large patch of orange, brown, or green in the Puget Sound is likely to be a "bloom," or gathering of marine algae or plankton. These are types of water plants and animals. Learn more about algae and other plankton. Report sightings to our scientists.

Algae facts

Phytoplankton are tiny plant-like organisms, also called algae. An algae bloom is the visible appearance of millions of phytoplankton in the water. Algae are present all year. However, sunshine, nutrients, and warm temperatures contribute to large seasonal blooms.

  • Algae blooms come in several colors
  • Algae can look like a pollution spill
  • Algae can produce toxins
  • Algae blooms effect oxygen levels in the water

Algae blooms come in varying shades of red, green and brown

View from seaplane showing reddish-orange mass of algae in Puget Sound.

Algae bloom in Budd Inlet viewed from a seaplane.

Algae blooms can appear in different colors ranging from green to red, orange, yellow or brown. Often these colors are from the pigments in different types of phytoplankton that allow them to photosynthesize.

Zooplankton that feed on the phytoplankton can also show as a bloom in the water. Noctiluca blooms are nontoxic and usually appear as a rusty reddish color like tomato soup. These blooms are common in Puget Sound.

For more on Noctiluca, see our publication: POSTER: Physical, Chemical, and Biological Conditions during Noctiluca Blooms in an Urban Fjord, Puget Sound Publication.

Algae can look like a pollution spill

Sometimes algae blooms look like spilled paint, oil, or sewage. Sometimes spilled contaminants can look like a bloom. Call if you are unsure.

Report an Environmental Issue tells what to do if you suspect that you are seeing pollution.

Algae can produce toxins

Most blooms are harmless, but some types of blooms can produce toxins that can make people sick if they are exposed to high enough levels of the toxins. Exposure can come from inhaling or swallowing water with toxins or from eating contaminated shellfish (that fed on the toxic phytoplankton).

The Shellfish Safety Information map at the Washington State Department of Health can tell the status of shellfish harvests in Washington.

Algae blooms effect oxygen levels in the water

View from above Puget Sound at Whidbey Basin with long dark purplish-black streaks in the water

Algae bloom in Whidbey Basin

Phytoplankton blooms are a natural occurrence in the spring. Blooms can also occur in summer and fall when there is an increase in nutrients from natural sources, such as wind-driven mixing of surface waters with deeper waters, or human sources, such as wastewater treatment plants. As phytoplankton use up the nutrients in the surface waters, their growth slows and cells eventually die.

Dying blooms can be an environmental concern because the cells sink and decay. Bacteria decompose the organic material, stripping oxygen from the water. This microbial oxygen demand, at times, leads to very low oxygen conditions in the bottom waters, possibly harming aquatic life.

We are taking steps in Puget Sound to determine how human activities and natural factors affect nutrient and low dissolved oxygen levels.

Let us know

Contact Dr. Christopher Krembs with reports of bloom sightings so that we can direct our oceanographers to those locations to collect and analyze samples, and keep statistical information on their occurrence. Please note the date, time, location, and color of the bloom.