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Highlights of the 2022 LLSA Water Team Findings and Call to Action-July 2023

Summary of the Verschoor Report:

Dr. Mark Verschoor (PhD Biology, York University, ON) prepared a detailed report “Monitoring and Determining the Source of Cyanobacteria Blooms in Leonard Lake” that reviews the 2022 LLSA Water Team Study dealing with a number of underlying concerns around water quality and lake health. The Verschoor report also briefly reviews historical investigations and studies. The report is technical in nature and this synopsis document is not intended to replicate the discussion. Readers seeking the full report and summary are encouraged to view those documents under the “Lake Health” tab, “Water Quality Studies” or at the bottom of this page.

Historical Background:

Leonard Lake is classified as an oligotrophic (low nutrient) lake. Generally, it was thought that such a lake would not experience algae blooms, yet the frequency of reported blooms not only in Leonard Lake but in other “low nutrient” Muskoka lakes has been rapidly rising in the past half decade. The report also provides historical evidence that indicates our water quality is declining.

Nuts and Bolts of the 2022 LLSA Water Study activities:

During the 2022 water testing season, intensive investigations were undertaken by members of the LLSA Water Team, with advice from Dr. Mark Verschoor. The aim of the testing work performed, was to gain a better understanding of the source and causes of the recurrent cyanobacteria blooms (blue-green algae), that have been detected yearly since 2017.

The 2022 Water Team investigations focussed on 3 primary areas of study:

  1. Water chemistry and algae sampling in summer and early fall at the same four deep spots as studied in the 2017 “Watson and Kling Study” - the objective being to determine changes and trends over the past five years which might contribute to a better understanding of algal bloom causation;

  2. Nearshore investigations in the areas where blooms have been detected, including microscopic determination of the bloom species, fluorimetry to detect and measure the telltale bloom species pigments, and any changes in nutrient level before or after the bloom event;

   3. Sampling of spring and fall run off points from 12 intermittent streams flowing into the lake to obtain an estimate of the nutrient 

       (phosphorus) and chloride (salt) levels.


The LLSA 2022 Water Study resulted in several important findings which strongly indicate, but do not fully confirm the source and cause of the blooms:

  1. Anoxia (no oxygen in the water) and internal loading (phosphorous and iron nutrient release from oxygen-free lake bottom sediments) were confirmed at both South Bay and the Mid-Lake site for the first time. The degree of anoxia and internal loading increased from July to September.

  2. Anoxia, but not internal loading occurred at the North Deep Hole site, while the Outlet Bay site remained free of anoxia.

  3. Deep chlorophyll maxima (elevated levels of chlorophyll) were found at the bottom of the euphotic (visible) depth (5-6m) at the sites where internal loading was occurring.

    Importance of (1) (2)and (3): The extensive anoxia, the presence of the bloom species (Dolichospermum lemmermannii) near the lake bottom, and the elevated nutrients at the time of nearshore blooms, indicates that the South Bay is a probable source of the blooms.

  4. The LLSA 2022 Water Study revealed the power of the recently purchased fluorimeter to easily and rapidly measure the telltale cyanobacteria pigment called phycocyanin and identify the pre-bloom conditions, the bloom itself, and the post bloom duration and intensity on our lake in 2022.

    Why is (4) important? The reaction time of the Spills Action Centre is often such that the telltale visual evidence of blooms has dissipated by the time personnel arrive to take samples. LLSA now has the capability to detect events in real time and continue to monitor, when stakeholders call in a potential sighting.

  5. Elevated levels of total phosphorus (up to 10 times the level in the lake),were found at several of the 12 runoff points. This indicates that the runoff may be an additional contributor of bloom nutrient. Chloride (salt) readings at runoff sites located closest to Highway 118 were very high, indicating that road salt is the primary contributor to increased salinity of Leonard Lake.

Recommendations in the Verschoor Report:

  1. Since the South Bay is the most probable source of blooms detected to date, further sampling should focus on this site to confirm this finding.

  2. Efforts should be made to track the movement of nutrient/bloom material from the South Bay site to determine if there is movement to areas along the Western shore where the blooms have been detected. Techniques could include using net hauls, fluorimetry and microscopic examination.

  3. Check for the abundance of the spiny water flea using net hauls and microscopy. This creature is an invasive species that if present will impact the number and health of algae eating zooplankton.

  4. Continue runoff studies, sampling both total phosphorus and chloride. Make efforts through additional analysis to track the source of the elevated nutrient flowing into the lake from the runoff points.

  5. Continue shoreline monitoring and“Eyes on the Lake’ reporting of suspected blooms.

  6. Continue to collect data from fluorometry and microscopic examination on samples to assess pre-bloom, bloom and post blooms conditions.

  7. Gather information, and investigate possible mitigation measures to address the anoxia in South Bay.

  8. It is probable that human activity and development are playing a role in bloom occurrence and deteriorating water quality on Leonard Lake. Continue to educate, inform and advocate for all who use the lake to undertake best practices to reduce their impact.

  9. Advocate for stronger locally developed policies to manage our lake health.


Call to Action

What does this mean as a lake stakeholder? What can I do to help?

No question that more study is required to fully understand what is going on, however, knowing what we now know, here are some important things we can all do to be sure we are pro-actively working towards a healthier lake.

  1.  Minimize hard surfaces on our properties – like patios, paved driveways, roof surfaces.

  2.  Examine the run-off routes from all hard surface areas and ensure the run- off from rain events makes its way to the lake as slowly as possible. “Vernal pools”- essentially spots where water rests and slowly seeps out and down through soils and rock, are the best way to handle run-off water.

  3. Consider an upgrade to an older septic system. Eventually an older system has to be replaced, and costs are always going up – why not do it now? New or old systems, keep chemicals, bleach, etc. out of your septic, and ultimately out of the lake. Have your septic system cleaned and inspected regularly (every 5 years).

  4.  Avoid disturbing lake bottom sediments that can contain layers of phosphorous and iron nutrient. That means not taking off in a larger boat from a near shore start – let’s practice deeper starts. Reduce speed especially in shallower areas of the lake.

  5.  Preserve and enhance that ribbon of life (the buffer area between land and water) with shoreline bushes and vegetation and additional tree cover to assist in filtering winter melt and rain-event run off.

  6.   Grass requires maintenance, and the use of “weed and feed” chemicals and/or fertilizer (phosphorus!) is tempting. Grass feeds the geese and we all know what that brings. Out with the grass and in with the real Muskoka look.

  7.  Do your part to keep the lake clean and unpolluted and invasive species out. Get rid of boat bilge and bait buckets on land; dispose of old oil, gas and chemicals responsibly. Don’t use soap or any chemicals to wash or shampoo yourself or clean a boat while in the lake or right next to the lake.

  8.   Keep motorized equipment – boat motors, personal watercraft, etc., in good working order to avoid water or air pollution. Still have a 2-stroke engine? Those motors can lose up to 30% of unused fuel into the water or the air through exhaust.

  9.   Be an advocate and guardian for lake health and set the standard for every one that visits/stays in your home or cottage.

Monitoring and Determining the Source of Cyanobacteria Blooms in Leonard Lake.
Mark Verschoor, PhD, Biology, York University, ON
April 2023.
Complete Report
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