Algal Bloom Alerts - Overview

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.

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. Bloom-forming conditions include:

  • sufficiently high levels of nutrients (phosphorus and to a lesser extent nitrogen)
  • calm weather and shallow or slow moving water flow
  • strong sunlight
  • high air & surface water temperatures

As there is an abundance of relevant literature covering the identification, reporting and relevant health implications, this introductory material has been limited to the above general information on algal growth and a list of key findings that would be relevant to Kahshe and Bass Lake.  A more detailed report on the Current Status of Algal Blooms in Kahshe and Bass Lakes, including factors that play a role in algal bloom development and on the health symptoms and use restrictions has been developed and is posted under this tab. Also posted in this section are several excellent references to help readers better understand the health and aesthetic implications of a harmful algal bloom and how the presence of a bloom needs to be reported.

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

  • On November 11, 2020, the Ministry of Environment, Conservation and Parks (MOECP) documented the first blue-green algal bloom in the vicinity of Oak Road (west end of the lake).
  • While this is the first documented blue-green algal bloom on Kahshe Lake, there have been an increasing number of blue-green 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.  This information is discussed in greater detail in the other posted document titled Current Algal Bloom Status for Kahshe and Bass Lakes – November 2020.

This section of the Lake Health tab will serve as a repository for any future algal bloom alerts and associated health advisories.

Ron Pearson

Kahshe and Bass Lake Steward - November 2020


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