This article was written by a Jefferson High School student in Melissa Hittner’s 2023-2024 AP Environmental Science class and edited by Friends of the Big Sioux River staff.

Whenever I go to Lake Madison, I make sure that I have an opportunity to jet ski. It is by far my favorite thing to do whenever I go there. The thrill of going as fast as I can and gliding off the waves of the lake is unlike any other, but when I docked the jet ski this last summer, I noticed something near the shore: several dead fish and plenty of algae.

The unpleasant sight of dead fish and algae made me wonder what was causing this troublesome occurrence. My first thought turned to what was coming into the lake that could harm it. I knew Lake Madison was a popular boating and swimming area. Perhaps the dead fish and overgrowth of algae were caused by human recreation in the water. After some research, I found out that this lake is a part of the Big Sioux River watershed. The small streams and creeks that flow into Lake Madison pass by farmland on their way to the lake. At its outlet, the water in Lake Madison flows into Round Lake, whose outlet flows into Brant Lake. It is important to note that urban and agricultural lands surround these three lakes.

One of the causes of fish kill is a decline in dissolved oxygen in a body of water due to increased algal blooms. When algae die, the decomposers perform cellular respiration, which requires massive amounts of oxygen from its environment. So, the nasty increase in algae was responsible for the fish kill. According to the South Dakota Department of Agriculture and Natural Resources, Lake Madison has excess nutrients, which are non-point pollutants that enhance algae blooms and cause fish kills. To determine the amount of algae present, a scientist can measure the Chlorophyll-a levels in a waterbody. After making this significant discovery, I decided to focus my research on these harmful nutrients and water quality indicators. In the article “Indicators: Chlorophyll A,” the Environmental Protection Agency mentions that water with a high concentration of nutrients from fertilizers often suffers from excess Chlorophyll-a. Since Lake Madison has a sizable amount of farmland surrounding its waters, fertilizers from nearby fields could have run into a creek that flowed into the lake.

I began to ponder potential solutions to this problem and considered the ecosystem services the lake provides. The lake regulates flood protection, supports biodiversity for countless plants and animals, generates revenue for the town from recreational activities, and is a beautiful and aesthetic body of water. Based on this information, I believe the best solution for reducing fish kills is to add riparian buffer strips along the sides of the creeks that feed into Lake Madison. Buffer strips are areas of vegetation separating cropland from waterways that reduce the effects of runoff and erosion on rivers. An article written by the Minnesota Department of Natural Resources claims that “Buffers may intercept or remove pollutants and sediment in the following percentages from runoff: 50 percent or more of nutrients and pesticides, 60 percent or more of some pathogens, and 75 percent or more of sediment.” While this would improve the water quality of Lake Madison, it has a positive impact on agriculture as well. These benefits include reduced erosion, flood protection, and reduced ditch maintenance costs. Another idea to reduce the runoff of nutrients is planting cover crops on farmland during the off-season. Cover crops are not necessarily for harvesting, but they provide many benefits, including improved soil health, reduced soil erosion, increased water retention, and more fertile land for future years. These practices would help Lake Madison because nutrients would stay on the agricultural land instead of running off into a nearby creek.

I dream of one day being able to hop off the jet ski and not having to watch my step for piles of algae or dead fish. I believe that implementing buffer strips and cover crops would be a step in the right direction and could save countless fish, improve agriculture, and improve the overall water quality of Lake Madison.