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

Kahshe and Bass Lake Water Quality

March 2024

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 have been conducted every other year for Kahshe and every third year for Bass Lake.  However, since both lakes were identified as 'Vulnerable' under the Muskoka Official Plan, the sampling of both has been conducted annually:

  • Total phosphorus in water at two mid-lake deep water sites on Kahshe (Main and Grant Bay) and one site in Bass Lake in May.
  • Water analysis for over 30 other chemical parameters at the above sites in May.
  • Secchi depth (water clarity) measurements in May and August at the above sites.
  • Temperature and dissolved oxygen readings 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 sites in both lakes from 2012 through 2023.

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 and chloride.

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 2023 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 2023 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

Algal Nutrients and Other Factors that Promote Algal Growth

Water quality monitoring of Kahshe and Bass Lakes by the DMM and the MECP has not identified any major water chemistry issues or trends in terms of algal friendly nutrients – phosphorus and nitrogen. Although both lakes have been classed as ‘Vulnerable’ under the updated Muskoka Official Plan (MOP), Bass Lake is expected to be removed due the findings of a DMM-funded Causation Study that identified natural causes as the reason for the elevated (>20 µg/L) levels of phosphorus, which is now one of three ‘Water Quality Indicators’ under the updated MOP.  Kahshe Lake remains on the ‘Vulnerable’ list due to the documented presence of harmful blue-green algal blooms (HAB) in both 2020 and 2021, although none have been recorded since then. While Bass Lake is slated to be removed from the ‘Vulnerable’ listing, it may be re-listed, as there was an HAB in 2023 and it remains on the Simcoe-Muskoka Health Unit’s active list.

Trends in water temperature, which can accelerate algal growth also were examined and there was no evidence of a warming trend in either lake based on water temperature measurements dating back to the early 1980s. Water clarity also has remained fairly steady over this four decade period, although clarity in Bass Lake is noticeably lower than in Kahshe.

And finally, it should be noted that the trend towards increasing numbers of HABs in Muskoka lakes continued in 2023, with 13 water bodies with documented HABs. This is cause for concern as the levels of algal-friendly phosphorus in Muskoka lakes have not increased over this time period. As such, changes in other factors that are known to accelerate algal growth and bloom development are happening. And, as we discovered in our Near-Shore Sampling Project in 2021, it is also possible that the historical sampling in mid-lake, deep water locations by the DMM and MECP is giving an excellent historical record of nutrient levels but not reflecting the elevated levels that have been documented in near-shore areas where algal blooms typically form.

Calcium Depletion

Decreasing lake water calcium concentration is an emerging concern for lakes on the Precambrian Shield in Ontario due to its impact on the reproduction and survival of zooplankton and other aquatic species that are important components of the aquatic food chain. The 2023 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 of 1.5 mg/L 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 since 2021. 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.

While the pH findings represent good news, it should also be recognized that the waters of Kahshe and Bass Lakes have low levels of alkalinity, and as such, are more susceptible to acidification as the ability of the water to buffer the acid input is low.

Metals and Other Chemical Contamination

The analysis of over 30 additional anions, cations and other chemicals by the DMM in 2023 has, with one possible exception, identified no trends or aquatic toxicity issues. While there were some minor exceedances of chronic (long term) 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.

In the case of aluminum, the aquatic benchmark has been exceeded in Bass Lake, with the highest concentration in 2023; however, the benchmark consists of a range in values and must be evaluated based on the pH and DOC concentrations in lake water. Based on these findings, the levels of aluminum need to be followed carefully in future monitoring to ensure that the waters of Kahshe and Bass Lakes are safe from an aquatic perspective.

The other finding from this data set is that there are numerous parameters that, like total phosphorus, are higher in Bass Lake compared to Kahshe Lake. There are also a couple of parameters (silicon and N-NO3) where levels in Kahshe are higher than in Bass. The reason for these differences in the two lakes is unknown and was not evaluated in the DMM-funded Causation Study on Bass Lake.

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 (referred to as being anoxic) also can cause mobilization (release) of phosphorus from sediments.

Dissolved oxygen is influenced by seasonal temperature changes that factor into lake stratification, the process whereby lake water is turned over (mixed) in the late fall and again following the winter ice melt and then begins to stratify through the spring, summer and early fall as water temperature increases at the surface and DO levels decrease with increasing depth.

As expected, the spring measurement of DO at increasing water depths in both Kahshe and Bass Lakes for 2023 revealed that with only one exception (Bass Lake >4m), DO was adequate for aquatic organism survival down to lake bottoms. However, by early August 2023, as in all previous decades, DO levels in Kahshe Lake fell below the aquatic health-based Provincial Water Quality Objective (PWQO) at around 4-5m depth and remain that way down to lake bottom (20m). In Bass Lake, by mid-August, the 2023 DO levels steeply declined beyond a depth of 2m and fell below the aquatic PWQO at depths greater than around 2.5m.

From a biological perspective, unlike Kahshe Lake, there appears to be a trend towards DO levels in Bass Lake falling below the PWQO at more shallow depths (just below 2m) than back in the 1980s and 1990s when DO crossed below the PWQO at depths almost at lake bottom (just below 3m).

Benthic Health

The presence of benthic organisms indicates the health of both the riparian and littoral zones, as these areas can be impacted by snowmelt, runoff, sedimentation and other shoreline development activities. Collected benthos are grouped into seven different categories based on their typical response to environmental contamination and are then compared to the Muskoka average from locations known to be remote from any shoreline development sources.

The 2023 assessment at two sites on Kahshe Lake confirmed that the benthic community is comparable to the Muskoka average for most family groupings, with the exception of % Chironimids and % EOT, where lower and higher benthic counts, respectively, are desirable outcomes. And, based on the benthic monitoring over the period from 2006 through 2023, there appears to be no increasing or decreasing trend in the various families of benthic organisms in Kahshe Lake.

Although the KLRA has not provided volunteer benthic counting support to the DMM for Bass Lake, we have been provided with the analysis results for 2023 and they revealed that the average (all years) index values for two sites on Bass Lake for %Chironimids are slightly lower than the Muskoka Average, and this is a good sign, as the species in this grouping are pollution tolerant. In the case of %EOT, the lower values relative to the Muskoka Average are not a desirable outcome, as these benthos are sensitive to pollutants. However, it was noted that in the case of %EOT, the 2023 findings do indicate a healthier outcome for this grouping that was masked in the averaging approach using data from all years. An evaluation of trends in benthic family groupings at both sites over time revealed no evidence of any trend in the health of these organisms over the period from 2016 to 2023.

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 HABs 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 HABs in the Oak Road area of Kahshe Lake on November 11, 2020 and in several locations in October 2021.  Bass Lake also has been impacted by a late-season HAB in 2023 and the health alert issued by the Simcoe-Muskoka Health Unit remains in effect.

    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.

    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

    Powered by Wild Apricot Membership Software