The key takeaways from the 2025 monitoring season are:
• Lake Fenwick's TSI values have dropped significantly since 2023. This is expected after the lake underwent an alum treatment in late 2023. In 2025, the TSI values were around the oligotrophic-mesotrophic range. Oligotrophic lakes (TSI <40) are very clear with low nutrient concentrations and low algal growth.
• Nitrogen-to-phosphorus (N:P) ratios were periodically above 25 for parts of the monitoring season. This indicates a low likelihood for the algal community to be dominated by cyanobacteria (which have the ability to produce toxins).
• Lake Fenwick had an alum treatment in late 2023. In 2024 and continued in 2025, we see the effect of this treatment with reduced phosphorus levels.
• An algal bloom was sampled for toxin testing in August. No algal toxins were detected in this sample.
This bathymetric map shows contour lines of equal depth, similar to a topographic map would for mountains and valleys. The red 'X' marks the location where water quality samples are taken.
This map shows the area of the watershed relative to the area of the lake. Generally speaking, the larger a watershed is relative to a lake, the greater the influence land use practices on lake water quality.
The average of these three TSI indicators during the growing season can be used
to place lakes in one of three broad categories:
<40 = oligotrophic (low productivity),
40 to 50 = mesotrophic (moderate productivity)
>50 = eutrophic (highly productive).
