Algal Bloom Status - Kahshe and Bass Lakes


Algae are simple, typically small aquatic organisms and range in structure from unicellular (a microscopic single cell) to multicellular and as they produce and grow, form colonies that appear on the surface or attached to various substrates. Algae are always present in lakes and rivers and are at the base (primary) of most lake food webs, and as such, are critical components of a healthy aquatic environment. Without algae, zooplankton (small animals that feed on algae) would not survive, and this would impact the survival of fish and other animals further up the food chain.

As identified in a Muskoka Watershed Guide document (MWC, 2017), there are three main types of algae that may potentially bloom in the Muskoka area:

Filamentous Green Algae

These are unicellular or multicellular and may form filaments that range from several millimetres to a metre in length. They can be found free-floating in shallow water on the bottom near shore or attached to submerged objects like rocks. They are typically green in colour, but can vary in shade depending on age and nutrient content. Some species form colonies that appear as cottony clumps, while others form thready, silky, slippery masses that are slimy to the touch. Blooms usually occur in the spring after heavy runoff or in the summer following hot spells and may appear as clumps or dense mats that float on or just beneath the surface of the water. Blooms can be a nuisance as they may produce a grassy or unpleasant. Bloom-forming filamentous green algae commonly found in Muskoka include: Spyrogyra, Zygnema, Mougeotia, Cladophora


Most are unicellular with a few species forming colonies. They are generally found in low-nutrient lakes and some can move vertically though the water column. Blooms usually occur in spring or early summer. Colonial species may form a bloom below the thermocline in stratified lakes and the water may appear cloudy or coloured. Other species may form a yellowish-green bloom in the upper layers of the lake that is highly visible. Blooms may produce taste-and-odour compounds often described as fishy, musty, or earthy. Bloom-forming chrysophytes commonly found in Muskoka include: Uroglena, Synura

Cyanobacteria (Blue-Green Algae)

These are actually bacteria, but have features in common with algae. Most are unicellular and often blue-green in colour. Some species can control their buoyancy to move vertically through the water column and position themselves for optimal light and temperature. Some species have the ability to produce toxins, making humans and animals sick if exposed to high concentrations. Blooms most commonly occur in late summer and early fall in areas where the water is shallow, slow moving and warm, but may also be present in deeper, cooler water. Blooms typically look like pea soup or spilt paint with a bluish or greenish colour. Fresh blooms often smell like freshly mowed grass, while older blooms may smell like rotting garbage. Gloeotrichia, which appears as “fuzzballs” about 2mm in diameter floating in the water column, may resemble tapioca on the lake surface when blooming. Bloom-forming cyanobacteria commonly found in Muskoka include: Anabaena, Aphanizomenon, Gloeotrichia

For anyone wishing to identify algal materials based on visual appearance, an excellent field guide has been published by Huynh and Serediak (2006).

Conditions that Promote Algal Blooms

When conditions are favourable, certain populations of algae can increase to levels that result in poor water quality and an algal bloom or scum may form. Conditions that promote bloom development include:

  • sufficiently high levels of nutrients (phosphorus and to a lesser extent nitrogen);
  • calm weather and shallow water with low flow;
  • strong sunlight; and,
  • high air and surface water temperatures

Nutrient enrichment and phosphorus in particular has been associated with increases in algal biomass in freshwater systems worldwide, and recent studies indicate that climate change is a potent catalyst for the further expansion of algal blooms because of the warming of surface waters. Rising air and water temperatures favour bloom-forming blue-green cyanobacteria because they have higher temperature requirements and because they are able to regulate their buoyancy under conditions of reduced vertical water column mixing (lake turnover) which occurs under rising surface water temperatures.

Algal Bloom Development in Ontario and Muskoka

In a 2011 publication (Winter et al., 2011), the Environment Ministry’s investigations of algal blooms in Ontario were summarized and their findings confirmed the following trends:

  • The total number of algal blooms reported in Ontario increased significantly from 1994 to 2009, and there also were significant increases in the number of blooms dominated by cyanobacteria and chlorophytes.
  • Most lakes (50) had a single bloom report, 11 lakes had blooms reported in two years, four lakes had reports in three years, and one lake had reports in eight of the years between 1994 and 2009.
  • In 2009, 16 of the 24 blooms reported tested positive for the presence of microcystin, one of several toxic substances which can be released by blue-green algal blooms.
  • A significant increase in day of year the last bloom was reported in a given year was observed, indicating that blooms are being detected and reported later in the year in recent years compared to 15 years ago. In contrast, no change was seen in day of year the first bloom was reported.

While this report only covered algal bloom development through 2009, the detection of toxic blue-green algal blooms has been confirmed by the Simcoe Muskoka Health Unit in six lakes in 2018 and eight in 2019 as identified in the following table.

List of Blue-Green Algae Impacted Lakes in the Neighbouring Muskoka Area-2018 and 2019

Affected Waterway


Date Public Notice Issued



Three Mile Lake

Muskoka Lakes

July 31, 2018

Lifted June 6, 2019

Clark Falls - Lake Rosseau

Muskoka Lakes

August 17, 2018

Lifted June 6, 2019

Boyd Bay - Indianhead Harbour, Lake Rosseau

Muskoka Lakes

August 21, 2018

Lifted June 6, 2019

Lake St. John


August 31, 2018

Lifted June 6, 2019

South West Bay - Leonard Lake

Muskoka Lakes

September 4, 2018

Lifted June 6, 2019

Lamont Creek


September 20, 2018

Lifted June 6, 2019


Three Mile Lake – Dee Bank Area

Muskoka Lakes

August 27, 2019

Lifted December 12, 2019

Brandy Lake – West end

Muskoka Lakes

September 12, 2019

Lifted December 12, 2019

Bass Lake – Northern end

Muskoka Lakes

October 24, 2019

Lifted November 26, 2019

Echo Lake – East end

Lake of Bays

October 11, 2019

Lifted December 12, 2019

Lake St. John


October 18, 2019

Lifted December 4, 2019

Lake St. George – South end


September 9, 2019

Lifted December 4, 2019

MacLean Lake - South end of Geri Bay


September 26, 2019

Lifted December 4, 2019

Why are Algal Blooms of Concern?

Blooms of cyanobacteria are of particular concern in freshwater systems because of the potential of many species to produce toxins (Winter et al., 2011). Those produced by cyanobacteria impact human and animal health and can affect freshwater ecosystem processes. They are generally classified into two groups:

  • neurotoxins and hepatotoxins, which can cause acute lethal poisoning; and
  • cytotoxins, which are not highly lethal to animals but show selective bioactivity.

Several species of cyanobacteria and chrysophytes also release noxious taste and/or odour-causing compounds that can have negative impacts on the public and the drinking water industry. For example, in the early 2000s, taste and odour events in Lake Ontario had major impacts on the drinking water provided to a large consumer population drawing from these sources and caused widespread public reaction.

The severity of symptoms and the level of risk to health depend on how you are exposed to blue-green algal toxins. Human health effects from contact with these toxins may include:

  • itchy, irritated eyes and skin from direct contact through activities such as swimming and water skiing, and
  • flu-like symptoms, such as headache, fever, diarrhea, abdominal pain, nausea and vomiting if large amounts of impacted water are ingested.

To give a better idea of the potential impact of a blue-green algal bloom, here’s a copy of the Health Unit’s 2018 advisory to the property owners on nearby Leonard Lake where a blue-green algal bloom was confirmed in 2018:

  • The health unit advises residents and businesses not to drink the water from this lake and to take the following precautions:
  • do not use the lake water for drinking or for food preparation including breastmilk substitute (infant formula), even if it is treated or boiled;
  • do not cook with the lake water because food may absorb toxins from the water;
  • do not allow pets or livestock to drink or swim in the water where an algae bloom is visible; and,
  • do not eat the liver, kidneys and other organs of fish caught in the lake and be cautious about eating fish caught in water where blue-green algae blooms occur.

The health unit advises residents and businesses not to drink the water from this lake and to take the following precautions:

Are Kahshe and Bass Lakes Susceptible to Algal Blooms?

The evaluation of algal bloom development by the Ontario Environment Ministry (Winter et al., 2011) included the following observations and conclusions regarding the susceptibility of Ontario lakes to algal bloom development:

  • Global increases in algal blooms have primarily been attributed to nutrient enrichment exacerbated by climate change.
  • General increases in human activity including cottage and residential development on and around the lakes in which blooms have been reported may have contributed to increases in nutrient inputs, promoting the growth of filamentous green algae and cyanobacteria.
  • The lakes from which blooms of cyanobacteria were reported were characterized by higher total phosphorus concentrations (15 µg/L) compared to a dataset from 1,074 Ontario lakes (9 µg/L).
  • However, the lakes in which the blooms were reported varied in total phosphorus concentrations, and 26% of the lakes were classified as oligotrophic, with less than 10 µg/L.
  • The development of cyanobacterial blooms in low nutrient lakes indicate that an array of other factors likely contributed to bloom occurrence. These included the availability of iron, phytoplankton community composition as well as environmental stressors including acidification and associated base-cation declines, the presence of invasive species, and climate change.
  • Climate change, specifically rising air temperatures, promotes conditions that favour cyanobacteria and the formation of blooms, including increased water temperatures, lengthening of the ice-free season, and reduced water column mixing.

Based on these findings of bloom development across Ontario, let’s look at our water chemistry and see if there are any signs of deteriorating quality. As shown in the adjoining chart of total phosphorus concentrations in Kahshe and Bass Lakes over the 39 year period from 1981-2019, total phosphorus has remained stable and very low on Kahshe while the total phosphorus levels in Bass Lake are about twice the levels in Kahshe, but fortunately, there is no evidence of increasing concentrations.

So what does this mean in terms of algal bloom development sensitivity for Kahshe and Bass Lakes?


Simply stated, our nutrient status, while remaining fairly stable across the monitoring period, is certainly within the range of total phosphorus reported in nearby lakes where toxic algal blooms have been documented. This is particularly true for Bass Lake, with concentrations of total phosphorus of around 20 µg/L.  And because of a documented changing climate and gradual increase in water temperatures that we have virtually no control over, we cannot rule out the possibility of an algal bloom on Kahshe or Bass Lakes. As such, our focus must shift to maintaining or even reducing nutrient levels.

It’s not complicated. The three contributors to nutrient loading where we can make a difference include:

  • Pumping out and having our septic systems (tanks/leaching beds) inspected on a regular basis
  • Managing our shorelines to keep them as natural and as vegetated as possible to minimize soil erosion directly into the lake, and;
  • Completely avoiding the use of phosphorus or nitrogen fertilizers on any existing lawns, gardens or flower beds in the vicinity of the shoreline.

To date, there has been no documented evidence of an algal bloom in either Kahshe or Bass Lakes. In the event we do experience an algal bloom, it needs to be reported to the Spills Action Centre of the MOECP. The phone number is: 1-800-268-6060. If the Ministry does identify it as a toxic blue-green or other type of toxic algae, the Simcoe/Muskoka Health Unit will investigate and issue health advisories regarding the health implications and conditions for use of the water for consumption and recreational purposes.


The key findings relevant to Kahshe and Bass Lake property owners/guests/users include:

  • §  To date, there have been no documented blue-green (toxic) algal blooms on Kahshe or Bass Lakes.
  • §  However, there have been an increasing number of toxic algal blooms detected in Northern Ontario, including lakes in Muskoka since the late 1990s.
  • §  This increase in impacted lakes appears to be associated primarily with increasing air and water temperatures associated with a changing climate but may also be due to a more informed public and reporting procedures.
  • §  In the event that a bloom is detected, it needs to be reported to the Spills Action Centre, Ontario Ministry of Environment, Conservation and Parks (MOECP). The phone number is: 1-800-268-6060.
  • §  If it is identified as a toxic blue-green or other type of toxic bloom, the Simcoe/Muskoka Health Unit will issue advisories regarding the health implications and conditions for use of the water for consumption and recreational purposes.

Literature Cited

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

Muskoka Watershed Council (MWC). 2017. Algae – Quick Guide. 1 page.

Winter, J.G., DeSellas, A.M., Fletcher, Heintsch, L., Morley, A., Nakamoto, L. and Utsumi, K. 2011. Algal blooms in Ontario, Canada: Increases in reports since 1994. Lake and Reservoir Management, 27:2, 107-114.

Ron Pearson

Kahshe and Bass Lake Steward

Kahshe Lake Ratepayers' Association (1994) Inc. (KLRA)
PO Box 1318, Gravenhurst, ON, Canada, P1P 1V5
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