What’s in Mankato’s Water?

Blue Earth County Soil and Water Conservation District has deemed nitrogen, phosphorus, and sediment as high priority issues that require conservation measures. But what are these substances and why are they harmful to our county?


Phosphorus is an important nutrient for plant life and animal growth. It can support the growth of algae and aquatic plants, these provide food and habitats for aquatic life. However, too much phosphorus in the water can stimulate algae to grow in excess amounts.

High quantities of algae can harm water quality, food resources, habitats and decrease the oxygen that fish and other organisms need to live. Large amounts of algae can also eliminate oxygen in water, causing illness and death to the water’s inhabitants.

The aquatic life is not the only ones impacted. High levels of phosphorus can harm humans as well.  Algal blooms can result from high phosphorus levels. Certain algal blooms can then produce toxins and bacterial growth that can cause illness if people come in contact or eat fish from the contaminated water. In addition, drinking this water can cause rashes, stomach or liver illness and respiratory problems.



Nitrogen, similar to phosphorus, is an important element. It can be found in the cells of all living things. Nitrates are a compound formed when nitrogen combines with oxygen or ozone. This compound can also be found in our water and cause health risks.

Similar to phosphorus, high levels of nitrates can cause oxygen depletion through excess plant and algae growth. Aquatic life that depends on a supply of oxygen will die as a result.

In humans, excessive nitrate contamination can restrict oxygen transport in the bloodstream. Infants who drink the contaminated water, if at high enough nitrate concentration, can become sick and even die. Blue baby syndrome is one of the negative impacts of nitrate-contaminated water. This condition causes a baby’s skin to turn blue because of decreased amounts of oxygen carried to different cells and tissues. Other illnesses from nitrates can range from miscarriages to stomach and gastro-intestinal cancer.

The Minnesota River has seen a spike in recent decades of nitrates in its water. This can pollute the aquifers the Minnesota River recharges. Therefore, affecting the drinking water. Runoff from chemical fertilizers, improper disposal of human and animal waste, unfortunate well location and construction are ways nitrates can enter bodies of water.

In 2018, with nitrogen issues rising, the Minnesota Department of Agriculture proposed the Groundwater Protection Rule. This rule’s main goal is to stop over-application and nitrogen leaching. It will limit the use of nitrogen fertilizer on some farm fields. The Groundwater Protection Rule is set to into effect January of 2020.



According to National Geographic, sediment is solid material that is moved and deposited in a new location. It can consist of rocks and minerals, as well as the remains of plants and animals. Sediment is a natural function of rivers and while it can be beneficial to farmland, problems can occur from large quantities of it, especially in water.

After a high-intensity rainfall, runoff from agricultural land, erosion of water banks and beds, and urban sources, like construction sites, can all result in high amounts of excess sediment.

Elevated sediment in the water can make the water muddy. This can affect waters aesthetics and swimming conditions. This muddy water can also inhibit natural vegetation from growing and make it difficult to clean for drinking water. The harder the water is to treat, the higher the cost is.

Sediment can also carry harmful nutrients, pesticides, and other chemicals into the body of water. Contaminated sediment can limit biological diversity and have a negative impact, similar to nitrates and phosphorous.












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