Water Quality

As recreational property owners and public users of the Kahshe and Bass Lakes, current and future water quality is one of the biggest concerns. Generally, Kahshe and Bass Lakes are healthy and thriving. However, as a community, we must remain vigilant in our overall lake stewardship as our waters are becoming warmer and are consequently becoming more prone to algal growth. Ongoing efforts to reduce nutrient inputs and improve other chemical indicators of lake health will be required to offset the anticipated effects of climate change.

Regular monitoring of water quality helps to ensure that the lakes are healthy and safe and provides information about how the ecosystem may be changing over time. This page provides details about the long-term monitoring programs that have been tracking physical, chemical, and biological water quality parameters since the 1980s.

Water Quality Monitoring Programs

Kahshe and Bass Lake are being monitored for long-term changes in water quality under two main initiatives.

Water Quality Overview

The detailed results of the water quality sampling programs for both lakes are provided in the annual Lake Steward Reports. Additional data is available in the KBLA-funded Near-Shore Water Sampling Project (NSWSP) that was carried out by the KBLA’s Conservation Committee in 2021. (Access historical reports here).  In general, the environmental quality of both Kahshe and Bass Lakes is evaluated based on six key indicators.

Phosphorus and nitrogen are vital nutrients that, when excessive, trigger algae growth, diminishing water clarity and harming aquatic life. Monitoring nutrient levels is crucial to maintain a healthy lake environment.

As can be seen in the charts below, algal-friendly nutrient levels of phosphorus have remained fairly stable over the four decades of sampling the mid-lake, deep water sites of both lakes by the DMM and MECP. The total phosphorus levels in Kahshe Lake are in the 10 ug/L range while those in Bass Lake are twice as high, averaging around 20 ug/L.

Total Spring Phosphorus (1983-2022): Kahshe Lake

Total Spring Phosphorus (1981-2022): Bass Lake

Similarly, the various nitrogen compounds in both lakes have remained fairly stable over this period. However, it has been demonstrated that the tracking of nutrients via these sites may not be providing a fully representative assessment of the sensitivity of the lake to harmful algal blooms, as the 2021 NSWSP demonstrated that in Kahshe Lake, much higher levels of both nutrients are present in the near shore environment.  A chart showing the results of the NSWSP for total phosphorus demonstrates the relationship between spring concentrations of total phosphorus at mid-lake deep water sites and those from near-shore locations in May, July, and September.

Similarly, the chart below shows how near-shore concentrations of ammonia-N, one of the nitrogen forms most closely linked with algal growth compared to mid-lake samples used to track historical trends in lake chemistry.

Although no harmful algal blooms (HABs) were identified in 2022, Kahshe Lake did experience HABs in both 2020 and 2021 and as such was identified as one of several Muskoka lakes deemed ‘vulnerable’ under the Muskoka Official Plan. Bass Lake also was declared a vulnerable lake but has since been removed from the list, as a DMM Causation Study conducted from 2020-2222 concluded that the elevated phosphorus in Bass Lake was not related to shoreline development, but rather due to several natural causes. A Causation Study has not yet been undertaken by the DMM on Kahshe Lake and as such, Kahshe Lake remains on the ‘vulnerable’ list of the Muskoka Official Plan. Based on these findings, we need to remain vigilant, as although there were no HABs on Kahshe in 2022, HABs were confirmed in 10 Simcoe and Muskoka area lakes in 2022. We also now know that higher levels of nutrients can be found in near-shore water where most HABs originate.

In summary, it is apparent that the mid-lake, deep waters of Kahshe and Bass Lakes are in good condition in terms of algal-friendly nutrients like phosphorus and nitrogen. However, as the 2021 Near-Shore Water Sampling Project in 2021 demonstrated, the annual spring sampling from mid-lake sites does not provide a fully representative assessment of water quality in the near-shore environment where algal blooms have been documented. The near-shore findings have shown that algal-promoting nutrient levels increase as the season progresses and appear to be related to accelerated leaching of phosphorus and nitrogen compounds from septic systems and managed lawns located close to the shore. 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. As property owners, 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.

Calcium is an essential nutrient for all living organisms and an important indicator of watershed health.

Unlike many other lakes in Muskoka, there is no detectable trend toward decreasing levels of calcium in either Kahshe or Bass Lakes. However, as levels of calcium are fairly close to the lower limit threshold that supports the growth of aquatic organisms, continued vigilance is necessary. This is underscored by the recurring late-season population explosions of Holopedium in Kahshe Lake since 2021. These pea-sized, jelly-like zooplankton thrive in low-calcium waters and although they are not known to be toxic, they are an uncomfortable nuisance as they can be felt against your skin while swimming. Read more about calcium trends and associated impacts in Muskoka Lakes here.

The pH of the lake water can affect the health of aquatic life. A pH between 6.5 and 8.5 is generally considered ideal for most aquatic species.

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.

The analysis of over 30 chemicals and water quality parameters by the DMM has identified no aquatic toxicity/health issues, and recent sampling has shown concentrations that are in the expected range for non-impacted surface water bodies in Ontario.

Dissolved oxygen is essential for fish and other aquatic creatures to survive. Fluctuations in dissolved oxygen levels impact the health of the lake’s ecosystem.

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 the 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 in terms of both aquatic health and phosphorus mobilization from sediment.

Sediment-dwelling invertebrates, such as worms, mollusks, and insects, are sensitive indicators used to monitor and assess lake 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 favorable findings. Read more about benthic monitoring in Muskoka Lakes here.