As the hardwater season comes upon us, so does the inevitable question, “why aren’t there drawdowns anymore?” It’s a complicated issue, always a good question, always with the same answer. I’ll try and keep it short!
There are two major reasons: 1) water quality, and 2) aquatic habitat (primarily Eurasian Watermilfoil). Let’s start with water quality. As you know, Tri Lakes were artificially created starting in the late 60’s and through the mid-70’s. Prior to the construction of the lakes, the area was a stream valley for the 14-Mile and Spring Branch Creeks. There was also a smaller lake called Deer Lodge Lake which is now the deep hole of Sherwood. At this time groundwater flowed naturally to the natural streams.
As the lakes were constructed, there was considerable dredging and filling to make “buildable areas”. Some of these areas are comprised chiefly of muck. The most extensive areas are along Camelot and Sherwood lakes. This buried organic sediment is very rich in nitrogen and phosphorus – nutrients that help aquatic plants and algae grow. After the streams were dammed to form the lakes, groundwater flow directions were drastically changed and even reversed in some areas. This results in groundwater flowing away from the lake or in a static situation. This is very prevalent towards the western side of each lake. This causes water to flow through the buried muck soils and away from the lake. When a drawdown occurs, groundwater reverses back to natural patterns and flows through the buried muck and then to the lake. As this occurs, groundwater releases large concentrations of nitrogen and phosphorus that it stripped from the buried muck, and releases these to the lake. This results in an additional pulse of nutrients to the lake, and it possibly explains why “internal loading’ is higher in Lake Camelot. The excess nutrient load from the drawdowns will decrease water quality and increase algae and plant growth.
Water level management such as drawdowns can be an effective tool to increase and diversify habitat. However, water level flux should match natural conditions, which they did not. In the case of Tri-Lakes, water levels are dropped much too late and raise much to soon for habitat improvements. In fact, what occurred was a decrease in native aquatic plants in the 0-3 foot range, which allowed invasive plants such as Eurasian Watermilfoil to recolonize and dominate the near shore area every year. Some native species weathered this change but did not compete well against the exotic and invasive Eurasian Watermilfoil.
There are other impacts to fish and wildlife as well. Any unnatural disturbance to the near shore area can have profound impacts. However, the two main reasons were the negative impacts to water quality and habitat. More information can be found in the Limnological Analysis of Tri-Lakes, Wisconsin (2002). U.S. Army Corps of Engineers, UWSP, WDNR.
Scott Provost – Water Resource Specialist