KAHSHE AND BASS LAKE WATER QUALITY

APRIL 2020

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 Ontario Ministry of Environment, Conservation and Parks (MOECP) 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 in May.
• Water sample collection for over 30 other chemical parameters in May.
• Secchi depth measurements collected in May and August.
• Temperature and dissolved oxygen readings collected from increasing water depths from the surface to the bottom of each lake in May and August. 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 (MOECP) 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 using a Secchi disc, and these findings are forwarded to the MOECP 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 MOECP where it is analyzed for 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 in posts that follow.

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 MOECP 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 2-3 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.

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, which are known to stimulate algal growth.
• Kahshe Lake is rated as a 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 below the 3-5 m typical depth for a Mesotrophic lake and more representative of clarity in a mildly Eutrophic 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 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 MOECP, 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, 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. We improve water quality and reduce the potential for algal blooms via these three actions:

• Pumping out and having our septic systems (tanks/leaching beds) inspected on a regular basis;
• Managing our shorelines to keep them as natural and as vegetated as possible to minimize soil erosion directly into the lake, and;
• 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 Lake Steward - March 2020