In 2024 Gary Nielsen and John Willson continued the water sampling that has been done annually for over 20 years. During the summer, forty-two phosphorus samples and water clarity recordings were collected over the period May 24th to October 30th inclusive; six samples from each of seven basins in the lake. The phosphorus test results from the Lake Partner program are not available yet.
Charleston Lake experienced good water clarity (Average Secchi depth 6.55m); this value is closer to the average 5-10 years ago, but considerably lower than last year when the water was unusually clear. When compared to the first five years (2000 to 2004 4.30m ) the improvement is remarkable. The largest part of the improvement in clarity is the result of the zebra mussel colonization of the lake. In 2024 Donaldson Bay had the highest average clarity at 8.00m, ranging to Goose Island at 5.50m average.
During this year’s testing on most occasions there were more suspended particles than seen in recent years. There could be several reasons for this, but we do know the surface water temperatures were abnormally high by end of May and sustained into Oct. We had great long swimming season, but that also helped algae grow. In September some sampling of the suspended particles was done. A variety of non-toxic algae were identified. Other factors we suspect impacted the clarity include the short ice cover season (ice formed mid Jan and went out in early March) which led to early stratification of the lake; generally sunnier and calmer weather that allowed more algae growth; a number of intense storms that caused excessive runoff; lake levels that were unusually high until late September which provided more opportunity for erosion from boat wakes.
Water clarity mean value for the 23-year period of record (6.27 m) places Charleston Lake in the oligotrophic category for the entire time frame, despite the fact that for the first five years of that period (2000 to 2004 inclusive) the water clarity averaged only 4.30 m. Oligotrophic lakes have a water clarity > 5.0 metres.
For comparison to other shield lakes and some local lakes the Lake Partner Program has produced a report with data up to 2023. It is on our website under Water Testing, Charleston Lake Data Report.
Every few years oxygen levels are tested from top to bottom at the same sites, mainly to assess the habitat for trout. Optimum habitat for trout is greater than 6 mg/L dissolved oxygen and less than 10C. Results were similar to previous years with optimal conditions throughout the season from depth of 12m to the bottom in Big Water, Deep Water, Eastern Reach and Donaldson Bay basins. Webster Bay and Goose Island areas were reasonable, better in the earlier part of the year.
Charleston Lake is improved from where it was a generation ago, but we have seen in the last year how things can start to change. Climate change is having impacts, so we need to look at what we can control, which is further reducing the nutrient load by focussing on healthy, runoff-absorbing shorelines, reduced fertilizer near the water, good functioning septic systems, and minimizing boat wake impacts.
John Willson and Gary Nielsen
