Bronte Wells
The St. Croix River is a popular destination for boaters and anglers and is known for its scenic beauty. It is one of the cleanest tributaries to the Mississippi River, thanks in part to a large forested watershed that helps filter out contaminants. However, the river is facing pollution threats, including increasing development and farm and urban runoff, which can cause algae growth and raise the temperature of streams, threatening aquatic life. The St. Croix has also been found to have concerning levels of PFOS, a chemical used in manufacturing, which has been detected in fish across the river. Additionally, the proposed Talon Metals nickel mine upstream of the river has raised concerns about sulfide mine pollution and increased mercury contamination of fish. While the river remains in good health, there are troubling trends that could impact its future cleanliness and ecological integrity.
| Characteristics | Values |
|---|---|
| Water Quality | Relatively good, low levels of bacteria |
| Bug Population | Thriving |
| Fish Population | Thriving, but unsafe to eat due to mercury levels |
| Mussel Population | Thriving |
| Phosphorus Pollution | High |
| Chloride Levels | Rising |
| PFOS Levels | Concerning |
| Sulfate Levels | May hinder the production of wild rice |
| Mercury Levels | High |
| Nickel Mining | Threatening |
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What You'll Learn
Mercury levels in fish
The St. Croix River is known for its scenic beauty and recreation opportunities for boaters and anglers. It is one of the cleanest tributaries to the Mississippi River, thanks in part to a large forested watershed that helps filter out contaminants.
However, the river is facing pollution threats, including increasing development and farm and urban runoff, which can cause algae growth. The stretch of the river from Taylors Falls to Lake St. Croix is considered impaired because of phosphorus levels. In addition, cities and industries discharge stormwater and treated wastewater into the river, which can contain pollutants such as chloride from road salt or water softeners.
Another major concern is the proposed Talon Metals nickel mine upstream, which could result in significant harm to the river due to the release of sulfate and toxic metals. The mine has control of 30,000 acres of minerals and has drilled as far southeast as the West Branch Kettle River. The National Park Service must ensure that the environmental impact statement for the mine considers the potential impacts on the river, including increased mercury contamination of fish.
Mercury is a well-known global pollutant and is present in trace amounts in all freshwater fish in the United States and likely worldwide. Elevated mercury levels in fish can be attributed to human activities that release mercury emissions into the environment. Mercury bioaccumulates within the tissues of fish and can have negative effects on human health, especially for those who regularly consume contaminated fish.
In 2021, scientists found elevated amounts of industrial chemicals called PFAS in the flesh of fish from the St. Croix River. The average amount in the fish sampled was 32 nanograms per gram, which is considered impaired and possibly harmful. The lowest level of PFAS detected was 1 nanogram per gram, still above the threshold. The chemicals originate from sources like 3M’s closed landfills in Oakdale.
Overall, while the St. Croix River remains relatively clean, it faces several threats that could impact the health of the river and the fish that inhabit it.
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Phosphorus pollution
The St. Croix River is a popular destination for boaters and anglers and is known for its scenic beauty. It is one of the cleanest tributaries to the Mississippi River, thanks in large part to a large forested watershed that helps filter out contaminants.
However, the river is facing pollution threats, including phosphorus pollution from farming and urban runoff, which can cause harmful algae blooms that kill fish and make certain sections of the river unsafe for swimming. According to a report by the Minnesota Pollution Control Agency (MPCA), while phosphorus pollution in the St. Croix River is declining, it still poses a threat to the river's health. The report also highlights the presence of toxic industrial compounds, such as per- and polyfluoroalkyl substances (PFAS), which are used in nonstick and stain-resistant consumer products.
The St. Croix River Association has also expressed concern about the river's health, noting that progress in reducing phosphorus pollution has been slow. They are working with officials in Minnesota and Wisconsin to keep the river on a "phosphorus diet" and meet water quality standards. The association's first "State of the St. Croix River" report found that concentrations of sediment, bacteria, and phosphorus had decreased slightly from 1976 to 2015, indicating a slow improvement in water quality.
Phosphorus occurs naturally but can be found in high concentrations in waste products and fertilizers. Urban stormwater and treated wastewater discharged into the river can contain phosphorus, contributing to the pollution problem. As the river gets closer to populated areas, the nutrient concentrations, including phosphorus, tend to increase, posing a greater threat to the river's health.
Overall, while the St. Croix River remains in relatively good condition, with thriving bug and fish populations and the presence of endangered freshwater mussels, the ongoing issue of phosphorus pollution needs to be addressed to ensure the long-term health and sustainability of this valuable natural resource.
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Chloride levels
The St. Croix River is a popular tourist destination for its scenic beauty and recreation opportunities for boaters and anglers. It is one of the cleanest tributaries to the Mississippi River, thanks in part to a large forested watershed that helps filter out contaminants.
However, the river is facing pollution threats, according to two new reports. The reports highlight some troubling trends, including increasing development leading to more polluted runoff entering the river. The Minnesota Pollution Control Agency’s study of the river’s health found that the St. Croix River is in good health, with low levels of bacteria and excellent fish and bug communities.
Nevertheless, the river is not entirely free of pollution. The MPCA report noted that levels of chloride in the St. Croix are relatively low but rising. Chloride contamination, from road-salt runoff and water-softener discharges, poses a threat to Minnesota’s freshwater fish and other species. The stretch of the river from Taylors Falls to Lake St. Croix is considered impaired because of phosphorus levels, which come from stormwater and treated wastewater discharged by cities and industries.
The St. Croix River also faces a potential threat from invasive species, such as zebra mussels and invasive carp. Additionally, the river has been contaminated by mercury, which has resulted in limits on how much fish from the river can be safely consumed. PFAS, or per- and polyfluoroalkyl substances, which are toxic industrial compounds, have also been found in the river. These chemicals are used in nonstick and stain-resistant frying pans, rugs, and countless other consumer products.
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Sulfide mine pollution
The St. Croix River is one of the cleanest tributaries to the Mississippi River. However, it is facing pollution threats, including increasing development leading to more polluted runoff, and high levels of phosphorus from farm and urban runoff.
The St. Croix River is also under threat from sulfide mine pollution. Talon Metals has control of 30,000 acres of minerals in the area and has drilled as far southeast as the West Branch Kettle River. The Talon Metals nickel sulfide ore mine would cause significant harm to the St. Croix River. The deposit is a "massive sulphide mineralization," with high levels of sulfide and metals, including nickel, cobalt, and copper, which are toxic to aquatic life. Sulfate released into the wetlands and sediments will increase the toxic contamination of fish, and mercury levels in fish are already a concern.
The National Park Service must ensure that the Minnesota Department of Natural Resources (DNR) conducts an in-depth environmental impact study of the entire "district-scale" mineral development that Talon Metals has described. The DNR has been criticized for prioritizing money over the environment, and it is easy for mines to get permits and expand their operations.
Community members and environmental organizations are calling for the National Park Service to protect the St. Croix River from sulfide mine pollution by influencing the environmental review of the Talon Metals mine proposal. They want to ensure that the river remains a treasured location for canoeing, kayaking, fishing, and swimming, with clean water and safe fish to eat.
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PFOS contamination
The St. Croix River has been contaminated with PFOS, or perfluorooctane sulfonate, a type of PFAS or "forever chemical". PFOS was found in high levels in fish from the river, with samples taken in 2017 and 2019 showing levels of up to 295 ng/g, far exceeding the safe level of 0.37 nanograms per gram. PFOS is known to accumulate easily in fish flesh and is believed to affect the development of fetuses and children, weakening immune systems and interfering with hormone levels.
The source of the PFOS contamination in the St. Croix River is attributed to industrial pollution, particularly from hazardous waste dumps operated by the company 3M. 3M manufactured PFOS for decades, using it in products like Scotchgard, non-stick coatings, and firefighting foam. The chemical waste was disposed of in landfills and dumps, some of which were located in areas that drained towards the St. Croix River. Over time, the chemicals leached into the groundwater and contaminated the river.
In addition to the St. Croix River, PFOS contamination has been detected in several other water bodies in Minnesota, including Clear Lake, Tanners Lake, Eagle Point wetland, and H.J. Brown Pond. The Minnesota Pollution Control Agency (MPCA) has proposed adding these water bodies to the state's impaired waters list, which already includes the St. Croix River due to previous mercury and PCB contamination.
While the river is still considered safe for swimming and recreation, there are now fish consumption advisories in place due to the PFOS contamination. The MPCA and other organizations are working to address the PFOS contamination and protect the health of the river and those who rely on it.
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Frequently asked questions
The St. Croix River is one of the cleanest tributaries to the Mississippi River. However, it is facing pollution threats.
The pollution threats to the St. Croix River include phosphorus from farm and urban runoff, which causes algae growth, and PFOS, a "forever chemical" used in manufacturing.
Pollution has impacted the health of the river, including fish populations. For example, there are concerning levels of PFOS in fish across the river, and the stretch of the river from Taylors Falls to Lake St. Croix is considered impaired because of phosphorus levels.
The Minnesota Pollution Control Agency (MPCA) is working to address pollution in the river. Additionally, there are calls for the National Park Service to protect the river from sulfide mine pollution, specifically the proposed Talon Metals nickel mine upstream.
