How to recognize an algae bloom

Last updated on May 12, 2022

Algae blooms come in many shapes and sizes, and harmful cyanobacteria blooms can look very similar to harmless algae blooms.

The only way to definitively identify a cyanobacteria or algae bloom is through microscopic analysis of cells at a certified laboratory. However, the following guide provides some basic guidance on recognizing and describing algae blooms.

First, determine whether the algae bloom type is filamentous or planktonic

You can do this with a simple finger test (or you can use a stick).  Wearing gloves, scoop up a handful of the bloom and let the water drain between your fingers.

Which image below most resembles the bloom you observed?

If "long stringy masses" are left on your hand,
it is filamentous algae.

filamentous algae (1)

If only "small bits" are left on your hand,
it is planktonic algae.

planktonic algae (1)

Second, find the descriptor that best defines what you are looking at

Once you have determined whether the bloom is filamentous or planktonic, use the identification table below to help determine the best descriptor for the bloom.

 

How to use the identification table

The table contains photo examples and descriptions of algal species that cause common algal blooms in B.C.

Some algal blooms may produce cyanotoxins (refer to "cyanobacteria bloom" column) and others do not (refer to "other algae bloom" column).

Review the photos and descriptions to help you determine which ones best fits what you are looking at and use this information to submit your observation to us.

 
1) Filamentous algae Cyanobacteria bloom Other algae bloom

Filamentous Algae example (1)

If you have observed a filamentous bloom, look to the right columns for further guidance on recognizing cyanobacteria versus algae. Then choose the appropriate descriptor option.

 

Examples of what you can identify

For this algae bloom type, you can either have:

  1. Filamentous algae that "Looks like stringy or net-like" and resembles the example under the cyanobacteria bloom column

    OR
     
  2. Filamentous algae that "Looks like stringy or net-like" and resembles the example under the other algae bloom column
 Descriptor option A: "Looks like stringy or net-like"
(see example images below)

oscillatoria species thumbnail (2)e.g. Oscillatoria

 

More details about Oscillatoria:

  • Can range in colour from green, blue, blue-green, purple or red
  • Can occur singly, or with other algal communities
  • Can be free floating, form mats, or attach to objects like rocks or logs.
  • Can produce microcystin (hepatotoxin) and anatoxin-a (neurotoxin)

 

cladophora algae thumbnail (1)e.g. Cladophora

 

More details about Cladophora:

  • Range in colour from green to yellow-brown to orange
  • Commonly found as colonies and long filamentous mats attached to rocks and stationary substrate
  • Can have a septic odour

 
 
2) Planktonic algae Cyanobacteria bloom Other algae bloom

Planktonic Algae example (1)

If you have observed a planktonic bloom, look to the right columns for further guidance on recognizing cyanobacteria versus algae. Then choose the appropriate descriptor option.

 

Examples of what you can identify

As an example, for this algae bloom type, you could determine that you have:

  1. Planktonic algae that "Looks like pea soup or paint-like" and resembles the example under the other algae bloom column

    OR
     
  2. Planktonic algae that "Looks like grass clippings" and resembles the example under the cyanobacteria bloom column

    OR
     
  3. Planktonic algae that "Looks like globular or bead-like" and resembles the example under the cyanobacteria bloom column

 

 Descriptor option B: "Looks like pea soup or paint-like"
(see example images below)

anabaena species thumbnail (3)e.g. Anabaena

 

More details about Anabaena:

  • Actually filamentous but does not form large colonies so appears as planktonic using the finger test. Especially prevalent in nutrient rich waters
  • Colour is usually green, or blue-green
  • Often has a noxious taste and odour
  • Can produce microcystin (hepatotoxin) and anatoxin-a (neurotoxin)

 

euglena species thumbnail (5)e.g. Euglena

 

More details about Euglena:

  • Colour can be green to red
  • Found in areas polluted by organic waste or decaying organic matter, and tend to have very dense populations

 
Cyanobacteria bloom Other algae bloom
or descriptor option C: "Looks like grass clippings"

aphanizomenon algae thumbnail (3)e.g. Aphanizomenon

 

More details about Aphanizomenon:

  • Primarily green in colour and resemble grass or green fingernail clippings
  • Some species can produce saxitoxin (neurotoxin) but species found in North American freshwater systems appear to be non-toxic but can cause skin irritations
  • Decaying blooms can release high concentrations of ammonia which can harm animals and cause fish kills

 

chlamydomonas algae thumbnail (6)e.g. Chlamydomonas

 

More details about Chlamydomonas:

  • Found in a variety of habitats including alpine snow
  • Elliptical-oval shaped solitary cells that can appear clumped together due to wind and wave action
  • Green to red in colour. Have a fishy smell when in high numbers

 
Cyanobacteria bloom Other algae bloom
or descriptor option D: "Looks like globular or bead-like"

nostoc algae thumbnail (4)e.g. Nostoc

 

More details about Nostoc:

  • Actually benthic but will appear as planktonic when using the finger test
  • Yellow-clear to blueish or olive green in colour, look like jelly balls
  • Can be dime to quarter sized, and can form colonies like bunches of “freshwater grapes” as they are sometimes called
  • Can produce cyanotoxins

 

volvox algae thumbnail (3)e.g. Volvox 

 

More details about Volvox:

  • Usually yellowish-brown to light green in colour
  • Individuals join together to form complex colonies, about 1mm in diameter
  • Colonies are surrounded by a gelatinous matrix

 
Cyanobacteria bloom Other algae bloom
or descriptor option E: "Looks like fluffy or pom-pom-like"

gloeotrichia algae thumbnail (3)e.g. Gloeotrichia

 

More details about Gloeotrichia:

  • Mature colonies are visible and look like tapioca beads or pom-poms
  • Generally buff or tan coloured, but can also be green or blue
  • Often found in hard water lakes
  • Generally recognized as non-toxic
  • Heavy blooms can cause skin irritations for swimmers

 

spirogyra algae thumbnail (7)e.g. Spirogyra

 

More details about Spirogyra:

  • Also called “water silk” or “frog spit”
  • Colour is a vibrant green shifting to yellowish-brown
  • Can be either attached or free floating and can form large mats
  • Dense mats can deplete oxygen, interfere with fishing, provide breeding sites for mosquitoes and clog filters and drainage areas

 

Please Warning symbolremember

If you suspect a cyanobacteria bloom on your water body, visit our cyanobacteria (blue-green algae) page and HealthLinkBC for more information.

 

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More identification tools and resources
 

Image references

(1) Algae identification - field guide : an illustrative field guide on identifying common algae found in the Canadian prairies / [by] Nancy Serediak and Mai-Linh Huynh. URL: http://publications.gc.ca/site/eng/9.694442/publication.html

(2) Source:  http://waterfeaturepros.com/pond-algae/oscillatoria-algae/

(3) Photos from B.C. Ministry of Environment and Climate Change Strategy staff files

(4) Source: http://www.downgardenservices.org.uk/bluegreenalgae.htm

(5) Source: https://www.britannica.com/science/Euglena

(6) Source: https://garden.lovetoknow.com/garden-basics/aquatic-plants/pond-algae

(7) Source: https://flisteward.com/2012/06/14/stewards-keep-eye-out-for-algal-blooms/