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Blue green Algae

Here are two very informative articles on blue-green algae (BGA):

The Algae of Kawartha Lakes - an excellent report commissioned by the Kawartha Lake Stewards Association in 2012, that provides great information on the types of algae that grow in Eastern Ontario lakes, when they become a hazard, and what controls their growth.  This information is equally relevant to Mississippi Lake. 




Blue-Green Algae    

By:  Kelly Stiles
Aquatic Habitat Biologist
Mississippi Valley Conservation Authority


This article on Blue-Green Algae appeared in the 2015 Edition of The Mississippi Belle.  It discusses Blue Green Algae events which occurred in the early fall of 2014. Similar algae blooms were observed in the early fall of 2015.

What are Algae?


Algae are naturally occurring aquatic organisms, similar to plants, which contain chlorophyll and produce their own food through photosynthesis.  Algae are present naturally in all lakes; however, they are often found at low enough concentrations that they are not noticeable to most people.  These organisms form a significant component of the base of the aquatic food chain.

There are many varieties of algae and a microscope or other laboratory techniques are often required to properly identify species.  Algae can generally be grouped into two easily identifiable forms:  filamentous, and planktonic.  Filamentous algae is very fibrous and when removed from the water resembles long stringy masses.  It can look like green cotton, smell like a pigpen, feel slippery or silky, or leave masses of “algae paper” on shore where it has dried out (Huynh and Serediak, 2006).  Planktonic algae has no fibrous structure and flows freely with the water.  The algae can stick to an item dipped in the water.  It can look like pea-soup, be globular, have a grassy odour, be a deep green or a green-black colour, or look like bright green foam (Huynh and Serediak, 2006).  Algae can also be classified under a variety of other categories including green algae, diatoms, flagellates, and blue-green algae.

What causes an Algae Bloom?


An algae bloom may occur when the right conditions combine to allow an existing population of algae to grow rapidly into a very large noticeable colony.  These factors typically include calm water, warm sunny conditions, shallow warm water and, usually, high nutrient levels (although in some cases this does not seem to be necessary).  Conditions ideal for a bloom usually occur in late summer and early fall; however, due to the effects of climate change this window may be shifting.  Keep in mind that due to the variety of algae species that may be present in a lake, algae blooms can appear in many colours including blue, red, brown or yellow, and in many forms and intensities.

What are the hazards associated with Blue-Green Algae blooms?


Although blooms may be caused by rapid growth of many different algae species, of significant concern for water users are blooms of blue-green algae (scientifically referred to as Cyanobacteria) which is actually a type of bacteria that contains chlorophyll.  Blue-green algae may produce a variety of toxins called microcystins, two of which are neurotoxins (brain toxin) or hepatotoxins (liver toxin), which can cause serious illness (Huynh and Serediak, 2006).  The Leeds, Grenville, and Lanark District Health Unit’s website describes the early symptoms from ingesting water containing toxic blue-green algae as “headaches, fever, diarrhea, abdominal pain, nausea or vomiting. Contact may cause rashes and mucous membrane irritation.” Ingestion of a large amount of the toxins is necessary before the liver and brain symptoms occur.


A blue-green algae bloom can typically be identified because the water looks bluish-green, like green pea soup, or turquoise paint (see photos).  When the blooms are very dense, they may form solid-looking clumps. Fresh blooms often smell like newly mown grass; older blooms may smell like rotting garbage (Ontario Ministry of the Environment and Climate Change website, 2014).


When certain blue-green algae species die or are damaged, their cells break down and toxins can be released into the water.  Laboratory analysis of water samples is the only way to confirm whether algae present in a bloom include the types that produce toxins, if toxins are present in the water and whether their concentration is cause for health concern.  However it is difficult to sample all parts of an algae bloom so if a blue-green bloom occurs a precautionary approach is best.

What should you do if you think you see a bloom?


It is important to report the bloom to the Ministry of the Environment and Climate Change’s (MOECC) Spills Action Centre Hotline (1-800-268-6060) as soon as you see it on your lake.  Everyone who witnesses a bloom should report it and not rely on their neighbour to do so.  This will give the authorities such as the MOECC and the Health Unit a clear scope of the extent of the bloom in order to better assess its potential impact.  Is it only happening in one bay or along one shore?  Or is it happening throughout the lake?  The MOECC will use this information and consult with the Health Unit to decide the amount of sampling by MOECC required to monitor conditions in the lake.


Since it is difficult to know for certain from the appearance of a bloom if it is composed of blue-green algae and only a laboratory test can confirm algae species and if microcystins are present at a concentration that could cause health problems, once you have reported a bloom you should use the precautionary approach and refrain from using surface water sources for drinking, washing, or swimming.  This includes restricting your pet’s interactions with surface water for drinking or playing.


The Leeds, Grenville and Lanark District Health Unit advises people using surface water for recreation and drinking to become familiar with issues concerning blue-green algae so they can make informed decisions on when to avoid contact with the water.  Algae blooms do degrade with time; however, it is not possible to say whether the toxins have completely left the area.  Once the toxin is released from the cell, where it goes is dependent on the local characteristics of water movement in the area.  The toxin will eventually be diluted into the body of water as any other soluble compound.  


If the MOECC receives laboratory results confirming the presence of toxin producing algae and microcystins they will notify the local Health Unit.  The Public Health Unit is working with the Mississippi  Lakes Association to develop an effective communication approach so all residents on the lake are notified if a bloom appears on the lake and the results of sampling.

Drinking Water


Surface water is never a safe source of drinking water without effective treatment.  The toxins released by blue-green algae are not removed by commonly used treatment methods such as boiling, chlorination or ultraviolet light treatment.  Consult a water treatment specialist if your drinking water comes from the lake.  You may want to choose another source of water for drinking.

Recreational Water Use


Avoid activities that increase your exposure to toxins in the water during an active algae bloom.  When deciding whether to resume recreational use of the water (swimming and water sports) after a blue-green algae bloom consider the following factors:

  • Faster moving water will dilute and move the toxins out of an area more quickly, further decreasing the risk to health.  Each property will have a different water flow pattern, so a local assessment is useful to further assess risk.

  • Skin irritation is the first sign that the level of toxins is significant in the water, so if this occurs it is important not to go in the water.  A few more days will help to clear the water if it is moving well, unless another bloom has occurred.

  • Be cautious about eating fish caught in water where a blue-green algae bloom has occurred.  Toxins are concentrated in the liver.  So avoid consuming the liver, kidneys and other organs of fish caught in an area affected by blue-green algae.

In addition to potential exposure to toxins from an algae bloom, lake users should be aware that the water in lakes and rivers always has the potential to be infected with bacteria, viruses and other microbes that can affect health. So it is important not to swallow the water. Young children are more likely to swallow water so it is critical to observe them carefully when in the water.

What Happened in Mississippi Lake in the Fall of 2014?


In September 2014 a number of lake residents contacted the MOECC, MVCA, and the Health Unit about a suspicious substance in the lake water that looked like either green pea soup or blue paint.  Anyone who contacted MVCA was encouraged to report their sighting to the MOECC hotline right away.


The MOECC came out to do a site visit and confirmed it was an algae bloom.  They took a water sample and sent it for analysis to determine what kind of algae was present in the bloom.  When the results returned from the lab, it was confirmed that it was indeed a blue-green algae bloom.  Although microcystins were found in the water sample, they were in concentrations below the Ontario Provincial Drinking Water Guideline’s maximum acceptable concentration of 1.5 µg/L.


No further action was taken at this point by the MOECC, Health Unit, or MVCA, and the Mississippi Lakes Association posted an update on their website.  This bloom helped to raise awareness of how to identify and report a bloom, as well as how to become a more educated and proactive lake user about potential hazards that could be in a surface water source of recreational and drinking water.

What is Mississippi Valley Conservation Authority Doing?


In order to identify and monitor problem areas and target stewardship actions, MVCA, Rideau Valley Conservation Authority and Carleton University, with funding from the Ontario Trillium Foundation, are developing an online tracking system to allow lake users to report algae blooms (the MOECC Hotline is the first priority for reporting, our tracking system will be used for other purposes), and changes in large aquatic plant beds (aka “the weeds”).  With the large number of lakes in our watersheds we are relying on our lake residents and lake users to help us collect this information by reporting what they are seeing on the lakes.  The website we have created for this project can be found at  We encourage lake users to report any changes they see on Mississippi Lake on this web site.  2014 was MVCA’s first year with the project so results are not yet available  but we hope that with your participation, we will have a useful tool to understand the extent, duration, and number of occurrences of blooms within a year and how that interacts with the extent of weed beds, presence of zebra mussels, and effects of climate change.

What Can Lake Residents Do?


We often hear from our lake residents that “these conditions have never happened like this in the past.” Scientists have found archival evidence to suggest that algae blooms may have occurred periodically dating back many years in some lakes.  Our partners at Carleton University are studying the lake bed sediments to help us assess the historic occurrence of algae in our lakes.


While we cannot control many of the conditions that lead to algae blooms, we can influence one of the factors that affect their growth; that is the nutrients available to them.  Property owners living on or near lakes and rivers can help by reducing or eliminating the use of fertilizers and soaps containing phosphorous, increasing the width and extent of vegetated buffer strips along shorelines, and ensuring that septic systems are fully functioning. 

Get the App


To report an algae bloom in real time, download the Android Citizen Water Watch App for your mobile device.  Snap a photo, fill in the information on time and location and upload it to the Water Watch site:

More information


For more information please contact your local public health unit or go online (see below):  


Leeds, Grenville and Lanark District Health Unit, Smiths Falls Office:
25 Johnston Street,
Smiths Falls, Ontario K7A 0A4
Phone: 613-283-2740
Fax: 613-283-1679
Office Hours:
Monday - Friday 8:30am - 4:30pm


Huynh, M. and N. Serediak. 2006. Algae Identification Field Guide. Agriculture and Agri-Food Canada. 40 pages.

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