Kahshe and Bass Lake Water Quality

May 2021

Kahshe Lake is being monitored for 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. 

Lake System Health Program

This program is operated by The District Municipality of Muskoka (DMM), with support from the Muskoka Watershed Council (MWC), the MECP and several other participating agencies.  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:

• Spring phosphorus sampling conducted at two 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 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 monitoring of Kahshe and Bass Lakes was conducted at established reference sites in both lakes from 2012 through 2018.

Lake Partner Program

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

The program consists of the following activities:

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 Grants Bay), using a Secchi disc, and these findings are forwarded to the MECP for compilation and comparison with other lakes in Ontario.

Water quality testing - Water is sampled from the same three 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 this water quality sampling for both lakes has been provided in the Lake Steward reports from 2012 through 2019 and in related Executive Summaries which are posted via links below. However, due to COVID-19, no sampling or analysis was carried out in 2020, and as such there is no Lake Steward Report.

Based on the findings from over 35 years of water quality sampling and analysis carried out every other year by DMM and every year for a more limited set of parameters by the MECP with the assistance of the Kahshe Lake Steward, the following conclusions regarding the water quality and biological health of Kahshe and Bass Lakes have been drawn:

Total Phosphorus

• Because of its importance in the growth and development of algal blooms, total spring phosphorus is measured by both programs.
• Kahshe Lake is currently at a level just below pre-established background concentrations and has shown no evidence of an increase or decrease over the 35+ years it has been analyzed.
• Total phosphorus concentrations in Bass Lake are about two times higher than in Kahshe Lake, but have not increased or decreased over the 35+ years; however, because Bass Lake levels exceeded 20 µg/L, the lake was flagged as a ‘Transitional Lake’ by DMM and has been sampled every year since 2016.
• Both lakes have been determined by DMM to be low in terms of responsiveness to phosphorus input.  However, because of limited soil attenuation potential, the phosphorus mobility rating is high.  The combination of these two factors results in a moderate sensitivity classification, meaning we need to stay vigilant in maintaining it at or below these levels.
• Another important factor which could influence the relationship between total phosphorus and algal blooms is lake temperature. DMM water temperature readings for the upper layers of both lakes appear to confirm the findings of others that have shown gradual warming of the upper layers of Muskoka lakes, and this has the potential to accelerate algal growth in combination with total phosphorus and nitrogen.

• In the 2019 Lake Steward report (posted below), it was noted that several lakes in the Muskoka area have experienced harmful blue-green algal blooms in 2018 and 2019. Although no blue-green algal blooms had been detected at the time the 2019 Lake Steward report was published (May 2020), a late season blue-green bloom was confirmed by the MECP in the Oak Road area on November 11, 2020 and information on its investigation and findings can be found via this link: Current Algal Bloom Status for Kahshe and Bass Lake-R2 Dec2020-Fin.

Although it no longer can be discussed in terms of a ‘likelihood’, it is still important to understand how the total phosphorus levels in Kahshe and Bass Lakes compare with levels in lakes where blue-green algal blooms have been documented. The chart to the left confirms that harmful blue-green algal blooms have developed in several of the impacted lakes that had total phosphorus levels well below those in Kahshe and especially Bass Lakes. Based on these findings, the presence of a blue-green algal bloom in November 2020 should not come as a surprise and this development underscores the importance of renewed efforts to drive our nutrient levels even lower than they currently are, as our climate is changing, and creating conditions that favour algal growth and bloom development.

As a result of the trend towards increasing numbers of harmful algal blooms in Muskoka, the DMM has now updated the Muskoka Official Plan to identify all lakes now considered ‘Vulnerable’ due to: a) the documented presence of an algal bloom, b) increasing concentrations of total phosphorus, or c) levels of total phosphorus in excess of 20 parts per billion. The impact of this vulnerable classification and the actions planned to address it can be found here.

Secchi Depth (Water Clarity)

• The clarity of water is affected by the amount of dissolved organic carbon (tea colouring) and also by increasing levels of nutrients such as phosphorus and nitrogen, which are known to stimulate algal growth.
• Kahshe Lake is rated as ‘moderate’ in terms of its dissolved organic carbon concentrations; however, based on the DMM and MOECP measurements over the years, the clarity level (visibility depth) is in the range of 2-3 m, slightly less than the 3-5 m typical depth for a Mesotrophic lake (a lake with moderate levels of nutrients and plant growth) and more representative of clarity in a mildly Eutrophic lake (a nutrient-rich lake).

Dissolved Oxygen and Water Temperature

• DMM’s evaluation of these two parameters has been ongoing for several years, and is important as both can have impacts on the health of aquatic receptors and, in the case of water temperature, on the potential for algal blooms.
• Based on the findings to date, the dissolved oxygen levels appear to be well within the normal and healthy range for most aquatic organisms and although some changes have been noted, they do not appear significant in terms of aquatic health.

Calcium and Acidity

• As calcium concentrations in Muskoka lakes has been decreasing because of improved pollution control on sulphur and other chemicals, there is concern that this could result in undesirable changes to water borne zooplankton species that require it and which are important in the aquatic food web.
• To date, the levels in both lakes are above the threshold for aquatic impacts, so this is a positive finding.
• Water acidity also is monitored and in both lakes, is well within the expected range.

Other Chemicals

• To evaluate the significance of the analytical results for a large suite of chemical parameters which have been analyzed for but not reported on by DMM, the data were assessed against surface water quality benchmarks set by the MOECP and other agencies to protect aquatic receptors (fish and other life forms found in fresh water) against impacts over long-term exposure periods.
• This analysis has confirmed that for all but two chemicals, the concentrations of these parameters are well below established aquatic benchmarks.
• For cadmium and copper, the analytical detection limits exceed established aquatic benchmarks. However, as the reported exceedances are assumed to be at the lab’s detection level, this is not considered to be of concern.

Conclusions from Water Quality Sampling

Based on the analysis of a large number of chemical and physical parameters by both the DMM and the MECP, it is apparent the waters of Kahshe and Bass Lakes are in reasonably good condition and compare favourably with the results for other Muskoka lakes. However, given the initial signs of increasing water temperatures which are consistent with the findings from other lakes in Muskoka, both lakes have now been classed as ‘vulnerable’ and will undergo DMM-funded Causation Studies. As such, we need to remain vigilant in our sampling efforts and overall lake stewardship, as warmer waters are more prone to algal growth and may negate potential improvements in nutrient enrichment and other chemical indicators of lake health. This has now been underscored by the confirmed presence of a blue-green algal bloom in the Oak Road area of Kahshe Lake on November 11, 2020. We can and must improve water quality and reduce the potential for future harmful algal blooms via these three main actions:

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

Ron Pearson

Kahshe and Bass Lake Steward - May 2021