Current Status: Not Impaired
Eutrophication or Undesirable Algae is no longer considered a concern within the St. Marys River Area of Concern.
The river’s strong connection to Lake Superior, combined with improvements in wastewater treatment and reductions in nutrient inputs over time, has helped maintain good water quality conditions. Monitoring has shown that nutrient levels, algae growth, and dissolved oxygen concentrations continue to support a healthy aquatic ecosystem.
The redesignation of this BUI reflects the success of ongoing environmental management efforts and confirms that the river is functioning as expected for a healthy Great Lakes connecting channel.
Why This BUI Was Listed
Eutrophication occurs when excess nutrients, particularly phosphorus, enter a waterbody and stimulate excessive plant or algae growth. In severe cases, these conditions can reduce water quality, decrease oxygen levels, and negatively affect aquatic ecosystems.
When the St. Marys River was first designated as an Area of Concern, concerns existed about nutrient inputs from municipal wastewater, industrial discharges, and urban runoff. Excessive nutrient loading had the potential to contribute to nuisance algae growth and other symptoms of eutrophication.
However, at the time there was limited information available to determine whether eutrophication was actually impairing the river. As a result, this beneficial use was initially identified as “Requires Further Assessment.”
Additional studies were needed to determine whether nutrient levels and algae growth within the St. Marys River differed from conditions expected in a healthy river system.
What Has Changed
Over the years, extensive monitoring was conducted to evaluate nutrient concentrations, water quality conditions, and aquatic plant and algae growth throughout the St. Marys River.
Researchers examined:
- Phosphorus and other nutrient concentrations.
- Dissolved oxygen levels.
- Water clarity and productivity.
- Aquatic plant communities.
- Algae growth and nuisance conditions.
- Comparisons with suitable reference locations.
The studies found that the river’s characteristics are strongly influenced by the large volumes of high-quality water flowing from Lake Superior. Nutrient concentrations were generally low and conditions associated with eutrophication were not observed at levels that would indicate impairment.
Monitoring also showed that dissolved oxygen levels remained sufficient to support aquatic life and that algae growth was consistent with natural conditions for the river.
The results demonstrated that the St. Marys River was not experiencing widespread eutrophication or nuisance algae problems attributable to human activities.
Status on the Canadian Side
On the Canadian side of the St. Marys River Area of Concern, assessments concluded that eutrophication and undesirable algae are not impairing ecosystem health.
Studies found that:
- Nutrient concentrations were generally low.
- Dissolved oxygen levels were adequate to support aquatic life.
- No widespread nuisance algae conditions were observed.
- Aquatic plant and algae communities were consistent with expected natural conditions.
- Water quality was comparable to suitable reference areas.
- Monitoring and assessment activities identified in the Remedial Action Plan were completed.
The available evidence indicated that nutrient enrichment was not causing environmental degradation within the Area of Concern.
Redesignated to Not Impaired on the Canadian Side
Based on the scientific studies completed for this beneficial use, Eutrophication or Undesirable Algae was officially redesignated to “Not Impaired” in 2018.
This redesignation reflects that:
- The assessments found no evidence of eutrophication-related impairment.
- Nutrient levels were not causing excessive algae growth.
- Dissolved oxygen conditions remained suitable for aquatic life.
- Environmental conditions were comparable to those expected in a healthy Great Lakes connecting channel.
- The assessment requirements identified through the Remedial Action Plan were successfully completed.
The redesignation confirmed that eutrophication and nuisance algae are not environmental concerns within the Canadian portion of the St. Marys River Area of Concern.