We have wrapped up what was an excellent year in 2024 from a water quality standpoint. We recently posted the final 2024 report of the Water Quality Monitoring Program on the SMLA website. This 83-page document, prepared by our scientist partners at Ferrum College, contains loads of detail about the water quality of SML. The overall conclusion is that we are very happy with the results in 2024. Here are some specific takeaways from this report.
The SMLA Water Quality Monitoring Program is comprised of a team of 53 citizen volunteers who donate their time and boat gas to venture out on the lake every two weeks in the summer to collect water samples and take water clarity readings. The result of their efforts provides a total of 1,176 data points each year for the past 38 years. We collaborate with a team of scientists at Ferrum College, who analyze the water samples collected by the volunteers, and take additional measurements of water temperature, pH, dissolved oxygen, conductivity, bacteria, and specific plankton species.
Three key metrics being measured through the SMLA volunteer effort are (1) phosphorus concentration, (2) chlorophyll-a concentration, and (3) water clarity. These metrics provide information on the overall health of the lake and over a period of years tell us if the lake is aging as it should.
Phosphorus – Our volunteers monitor 56 locations on the lake for phosphorus, every two weeks during the summer, for a total of 336 data points. While
phosphorus is an important nutrient for all life, too much of it in the lake can result in excess growth of algae. After hitting an all-time high in 1999, the levels of phosphorus in the lake have been steadily decreasing to a level in 2024 that is 8% lower than the 20-year average. This is a very good result!
Chlorophyll-a – As stated above, phosphorus can lead to excess algae growth. We measure algae growth by sampling the concentration of chlorophyll-a. Every two weeks our volunteers monitor the same 56 locations on the lake for chlorophyll-a, collecting a total of 336 data points. As the accompanying graph shows, this metric can be very volatile from one year to the next, due to variations in temperature, precipitation, and nutrients such as phosphorus in the water. It is no coincidence that 2024 was one of the best (lowest) years we’ve seen in the past 20 years for chlorophyll-a.
Water Clarity – Water clarity is a measure of the concentration of small particles floating in the water, which includes suspended dirt, silt, and algae. This measure is usually most sensitive to algae growth, though it may also be adversely impacted by excess boat traffic or silt runoff from heavy rains. Every two weeks our volunteers monitor 84 locations on the lake for water clarity, collecting a total of 504 data points during the summer. For 2024 the average water clarity was about 5% higher (clearer) than the 20-year average.
Throughout the monitoring season we post the results of the bi-weekly monitoring on the SMLA website, in the form of circular speedometer-like gauges that provide visual context of whether the results are considered favorable or not. Until now, these gauges have been limited to showing average results for the lake as a whole. We have heard your feedback that you would also like to see results for selected areas on the lake, recognizing that there can be significant variation from one area to the next. We have been working on adding this capability to the SMLA website, and we hope to have it in place in time for the opening of our 2025 monitoring season in late May.
