[[Links to detailed annual Lake Steward reports are at the bottom of this page.]

Kahshe and Bass Lake Water Quality

April 2023

Update August 2023: Information about the Bass Lake Causation Study has been added to the bottom of this page.

Kahshe Lake is being monitored for long term changes in water quality under two main initiatives as outlined below. Because of its smaller size, the water quality program for Bass Lake is limited to the more comprehensive Lake System Health Program

DMM - Lake System Health Program

This program is operated by The District Municipality of Muskoka (DMM).  For Kahshe and Bass Lakes, the DMM program consists of the following activities which are conducted every other year for Kahshe and lately, every year for Bass Lake:

  • Total phosphorus sampling conducted at two mid-lake deep water sites on Kahshe (Main and Grants Bay) and one site in Bass Lake in May.
  • Water sample collection for over 30 other chemical parameters at the above sites in May.
  • Secchi depth (water clarity) measurements collected in May and August at the above sites.
  • Temperature and dissolved oxygen readings collected from increasing water depths from the surface to the bottom of each lake in May and August at the above sites. and;
  • Benthic invertebrate monitoring of near-shore sediments of Kahshe and Bass Lakes at established reference sites in both lakes from 2012 through 2018.  This was re-commenced in Kahshe Lake in 2021 as groundwork for a Causation Study which will be undertaken by the DMM at a later date.

MECP - Lake Partner Program

This program is operated by the Ontario Ministry of Environment, Conservation and Parks (MECP) through the Dorset Environmental Science Centre.  Under this program, water sampling and measurement of water clarity is conducted by the Kahshe Lake Steward every year as shown below:

  • Water clarity measurements
    • Clarity of the water is measured every two weeks during the ice-free period at three locations (Deep Bay, Kluey’s Bay and Grant Bay, using a Secchi disc, with these findings being forwarded to the MECP for compilation and comparison with other lakes in Ontario.
  • Water quality testing
    • Water is sampled from the same three mid-lake locations in May each year and sent to the MECP for analysis of total phosphorous, an indicator of the potential for algal blooms and nutrient enrichment and for calcium.

Summary of Water Quality Findings

A detailed report on the findings of these two water quality sampling programs for both lakes has been provided in the Lake Steward reports covering sampling from 2011 through 2022 and in related Executive Summaries which are posted via links below.  In addition, the KLRA funded a Near-Shore Water Sampling Project (NSWSP) that was carried out by the KLRA's Conservation Committee in 2021, and finding from that report are discussed and referenced below.

Due to COVID-19, no sampling or analysis was carried out in 2020, and as such there was no Lake Steward Report.

In the 2022 Lake Steward report, the environmental quality of both Kahshe and Bass Lakes was evaluated on six key indicators, and the findings are summarized below.

Water Quality Indicators

Key Findings

Nutrients and Other Factors that Promote Algal Growth

With one exception, algal friendly nutrient levels of phosphorus and nitrogen have remained fairly stable over the four decades of sampling the mid-lake, deep water sites of both lakes by the DMM and MECP. However, it has been demonstrated that the tracking of nutrients via these sites may not be providing an accurate picture of the sensitivity of the lake to harmful algal blooms, as an earlier 2021 KLRA-funded study of near-shore nutrient loading on Kahshe Lake has demonstrated that higher and more variable levels of both nutrients can be found in the near shore environment.  Although no harmful algal blooms (HABs) were identified in 2022, we need to remain vigilant, as HABs were confirmed in 10 Simcoe and Muskoka area lakes in 2022 and because of higher levels of nutrients that can be found in near-shore water. Based on the linkages between HAB development and a changing climate, an action plan for all shoreline property owners has been developed and follows this summary table.

Calcium Depletion

The 2022 data confirm that there is no detectable trend towards decreasing levels of calcium in either Kahshe or Bass Lakes. However, as levels of calcium are fairly close to the aquatic growth limiting threshold and as this threshold value would not be protective of all aquatic organisms, continued vigilance is necessary. This is underscored by late season population explosions of Holopedium in Kahshe Lake in both 2021 and 2022. These pea sized, jelly-like orbs are not known to be toxic, but are an uncomfortable nuisance as they can be felt against your skin while swimming.

Lake Acidification

The waters of Kahshe and Bass Lake have acidity (pH) levels that are within a normal range and there is no evidence of an increasing or decreasing trend in acidity over the two decade monitoring period.

Metals and Other Chemical Contamination

The analysis of over 30 additional chemicals and water quality parameters by the DMM in 2022 has identified no aquatic toxicity/health issues. While there were some minor exceedances of chronic (long term) aquatic health protection benchmarks established by the MECP and other agencies in the early years, most of these exceedances were likely due to sampling or laboratory artifacts, as more recent sampling has shown concentrations that are in the expected range for non-impacted surface water bodies in Ontario. The only exception was for aluminum in Bass Lake, where the aquatic benchmark has been exceeded in several years; however, this is unlikely to be of concern as confidence in the benchmark is low due to complicating factors that were identified in its derivation.

Dissolved Oxygen Depletion

Dissolved oxygen (DO) in lake water is important, as it is essential for the survival of all aquatic organisms. A lack of oxygen in the lower layers of the lake also can cause mobilization (release) of phosphorus from sediments.

In Kahshe, the DO levels follow the historical trend of falling below the PWQO (a level below which some aquatic organisms may be at risk) at a depth of around 5m below the surface. However, unlike the earliest data from the 1980s and 1990s, they begin gradually recovering (increasing) in 2022, following the trend that was observed in the 2000-2009 and 2010-2019 decades. This is good news in terms of aquatic life at lower depths of the lake.

In Bass Lake, by early August, the 2022 DO levels are essentially similar to the historical records of DO levels down to about 2m depth and then decrease gradually through the 3m depth, falling below the PWQO just below the 2m depth. This is a concern from both an aquatic health and phosphorus mobilization from sediment perspective.

Benthic Health

Benthic health assessment is now undertaken annually, as Kahshe Lake is now considered a ‘Vulnerable’ lake due to the appearance of HABs in 2020 and 2021. Collected families of benthic invertebrates are grouped into seven different categories based on their typical response to environmental contamination and are then compared to the Muskoka average. The 2022 findings confirmed that species richness (biodiversity) was good and that species that thrive in good water quality were above the Muskoka average while species that thrive under pollution stress were below the Muskoka average, both of which are favourable findings.

As noted above, given the impact that HABs can have on the recreational enjoyment and property values of the lake, the KLRA funded a Near-Shore Water Sampling Program that was designed by the Conservation Committee and implemented in 2021. A full description of the Near-Shore project can be found HERE .  A full report, as well as an Executive Summary, of the findings can be found by clicking the links.

    Conclusions from Water Quality Sampling

    Based on the analysis of a large number of chemical and physical parameters by the DMM and MECP, it is apparent the mid-lake, deep waters of Kahshe and Bass Lakes are in a reasonably good condition in terms of algal-friendly nutrients like phosphorus and nitrogen. However, as the Near-Shore Water Sampling Project has now shown, the quality of Kahshe Lake water which has been based on spring sampling from mid-lake sites is not providing a realistic assessment of water quality in the near-shore environment where algal blooms have been documented. The near-shore findings have clearly demonstrated that algal-promoting nutrient levels increase as the season progresses and appear to be related to accelerated leaching of phosphorus and nitrogen compounds sourced from septic systems and managed lawns located close to the shore.  Although more evidence is warranted, the appearance of late season HAB appears to be related to precipitation events associated with our changing climate.  The Near-Shore project findings have been examined by the Conservation Committee to determine if there are additional follow-up actions shoreline property owners can take to mitigate the impacts on near-shore waters. These follow-up actions can be found here.  The findings will also inform the design and conduct of the DMM-funded Causation Study that will proceed when funds are available.

    Based on the above water quality findings, we need to remain vigilant in our sampling efforts and overall lake stewardship, as climate changes, including more intense rainfall events, appear to be increasing the migration of algal friendly nutrients from our shorelines to the near-shore water. This has been underscored by the confirmed presence of blue-green algal blooms in the Oak Road area of Kahshe Lake on November 11, 2020 and in several locations in October 2021.

    In summary, we can and must improve water quality and reduce the potential for future harmful algal blooms by the actions identified in the "How Can We Help" document referenced above.  These actions have been further condensed below:

    1.  Divert roof drainage and runoff from paths and other hard surfaces away from your septic system and the shoreline. If necessary, direct rain water into rock-filled drainage pits.

    2.  Keep most of your shoreline as natural as possible with a zone of trees, shrubs or tall grass between the shore and any lawn area to discourage grazing by Canada geese and to reduce soil & goose poop runoff into the lake.

    3.  Have a licensed professional pump out and inspect your septic system for failures and deficiencies every 3-5 years and more often for aging systems installed pre-2000. The Town will be inspecting in 2023, but we don’t need to wait until then and be subject to system shutdown until failing systems are repaired.

    4.  Don’t use phosphorus or nitrogen fertilizers or cleaning agents anywhere near the shore.

    Bass Lake Causation Study

    The final report of the District Municipality of Muskoka's (DMM) 'Causation Study' on Bass Lake has been released. This study was undertaken by a team of environmental consultants who were retained and funded by the District. Bass Lake was placed in the 'Vulnerable' Category due to elevated levels of total phosphorus, a primary nutrient involved in the development of Harmful Algal Blooms (HABs). Some key findings and outcomes are summarized below:

    • The causation study concluded that the cause for the elevated phosphorus concentrations in Bass Lake cannot be reliably determined with the current (historical) information. 
    • There was no evidence of changes in waterborne phosphorus concentrations in the lake over time, suggesting that recent development and land use changes (from 2008 through 2018) have not significantly altered phosphorus levels in the lake. 
    • Long term elevated phosphorus concentrations in Bass Lake were concluded to be the result of several possible natural influences, including:
        • a large watershed to lake area ratio combined with a small and shallow lake;
        • prolonged periods of low oxygen levels in the water at the bottom of the lake resulting in the release of phosphorus from sediments
        • the release of phosphorus from adjoining wetlands
    • KLRA comments on the draft report back in 2022 highlighted the very limited sampling program that was undertaken during the two year period of the study as a supplement to the regular DMM sampling. Our comments have been summarized in Appendix F (pgs. 114-117) of the report and unfortunately, most were deemed to be beyond the scope of the consultant's work plan.

    As the Causation study on Bass lake confirmed that development was not the cause of the elevated phosphorus levels, Bass Lake has now been removed from Schedule E2 of the Muskoka Official Plan (MOP) and is therefore, not subject to the Enhanced Protection Policies, as outlined in Section C2.6.6. of the MOP. 

    Ron Pearson, M.Sc.

    Kahshe and Bass Lake Steward

    Kahshe Lake Ratepayers' Association (1994) Inc. (KLRA)
    PO Box 1318, Gravenhurst, ON, Canada, P1P 1V5
    Information: info@kahshelake.ca      Site Comments: webmaster@kahshelake.ca

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