Identifying Cyanobacteria (Blue-Green Algae) Blooms
Introduction
Cyanobacteria, also known as blue-green algae, are a type of microscopic photosynthetic organism classified as bacteria. Under certain conditions, cyanobacteria can rapidly reproduce to form a “bloom.” A bloom is a dense, visible growth of cyanobacteria that may discolor the water, reduce water clarity, and form a scum. Cyanobacteria blooms can (but do not always) produce toxins that are harmful to humans, pets, livestock, and wildlife.
This guide is meant to help you identify what a cyanobacteria bloom may look like so that you, your family and your animals, can avoid cyanobacteria blooms while recreating. If you suspect that you see a cyanobacteria bloom the best course of action is to keep people and animals out of the water and report the bloom to RIDEM by emailing DEM.OWRcyano@dem.ri.gov.
Identifying a Bloom
Cyanobacteria blooms often occur in freshwater during the summer and fall but can occur year-round. Blooms often vary in appearance and may display the following properties:
- Blooms are usually bright green or blue in color but may also be red, brown or yellow.
- Water may resemble pea soup or be cloudy with a green tint.
- A green scum may form on the shoreline.
- May appear as if paint has been spilled on the surface of the water.
- Green streaks and swirling may cover the surface of the water.
The following photos display cyanobacteria blooms with a variety of appearances and colors. The last section shows examples of some "cyanobacteria look-alikes", which are aquatic plants that resemble cyanobacteria but do not produce toxins.
The photos above show examples of cyanobacteria blooms with a "pea soup" or cloudy, green appearance.
The photos above show examples of a shoreline scum associated with cyanobacteria blooms.
The photos above show examples of cyanobacteria blooms with a spilled paint appearance.
The photos above show clumps of cyanobacteria.
Cyanobacteria Look-alikes.
Here are some examples of aquatic plants and pollen that are often mistaken for cyanobacteria blooms.
Duckweed (right) and watermeal are small floating plants that may look like cyanobacteria from a distance but can be distinguished when viewed up close.
Each individual duckweed or watermeal plant is clearly visible to the naked eye whereas cyanobacteria are microscopic. The photo on the right is a close-up view of individual duckweed plants.
Pollen (right) may be mistaken for cyanobacteria in the spring, when it may form a yellow film on the water's surface. It can be difficult to tell the difference between pollen and cyanobacteria so it's best to report it to RIDEM if you're not sure (DEM.OWRCyano@dem.ri.gov).
Filamentous algae will typically clump like hair. Cyanobacteria may appear as small clumps in the water, but they do not form long thread-like strands.
For more information about cyanobacteria, visit RIDEM's Cyanobacteria Website .
To report a cyanobacteria bloom, email DEM.OWRCyano@dem.ri.gov.
