Current Status: Impaired

Fish Tumours or Other Deformities remains one of the remaining Beneficial Use Impairments in the St. Marys River Area of Concern.

Although many environmental conditions have improved and numerous cleanup actions have been completed, tumour rates in white sucker continue to exceed the established delisting criterion. Ongoing monitoring, sediment remediation, and scientific investigation are helping to identify the remaining factors contributing to this impairment and guide future restoration efforts.

Why This BUI Was Listed

Fish Tumours or Other Deformities was identified as impaired because studies found elevated rates of liver tumours in white sucker, a bottom-feeding fish commonly used as an indicator of environmental health.

Between 1985 and 1990, researchers examined 185 white suckers collected from the St. Marys River and found a tumour prevalence rate of 9.2%. This exceeded the Great Lakes guideline of less than 5%, indicating that environmental conditions within the Area of Concern may have been affecting fish health.

Scientists suspected that exposure to contaminants in river sediments, particularly polycyclic aromatic hydrocarbons (PAHs), contributed to the development of these tumours. PAHs are chemicals historically associated with industrial processes such as steel production and the combustion of coal and petroleum products.

Because tumour rates were significantly higher than acceptable levels, Fish Tumours or Other Deformities was listed as a Beneficial Use Impairment when the St. Marys River was designated an Area of Concern.

What Has Changed

Over the past several decades, substantial efforts have been made to reduce contaminant inputs to the river and better understand the causes of fish tumours.

Several remedial actions have been completed, including:

• Process improvements at major industrial facilities to reduce contaminant releases.
• Investigations into contaminant sources throughout the watershed.
• Development of sediment management plans and contaminated sediment assessments.
• Ongoing monitoring of fish health and sediment quality.
• Environmental dredging and remediation efforts within the Algoma Boat Slip.

These actions have helped improve environmental conditions within the river. In 2015, a study of 100 white suckers found a tumour rate of 6%, representing a notable improvement from earlier assessments.

However, more recent monitoring has revealed that challenges remain. Between 2021 and 2023, researchers collected and examined 147 white suckers from locations throughout the Area of Concern. Sixteen fish were found to have tumours, resulting in a tumour prevalence rate of 10.9%.

To better understand these unexpected results, a sediment chemistry investigation was completed near St. Joseph Island in 2025. The study found no elevated concentrations of PAHs in the area, suggesting that additional research is needed to determine why tumour rates remain above the established threshold.

Status on the Canadian Side

On the Canadian side of the St. Marys River Area of Concern, Fish Tumours or Other Deformities remains classified as Impaired.

Current assessments show that:

• The tumour prevalence rate remains above the delisting criterion of less than 5%.
• Recent monitoring found a tumour rate of 10.9% in white sucker.
• Sediment investigations have not identified elevated PAH concentrations in some areas where fish with tumours were collected.
• Most of the remedial and monitoring actions identified in the Remedial Action Plan have been completed.
• Work continues to better understand potential contaminant sources and fish exposure pathways.

Because the cause of the elevated tumour rates is not yet fully understood, additional investigation is required before this BUI can be redesignated.

What Happens Next?

The Remedial Action Plan team is continuing to investigate why tumour rates remain elevated despite significant environmental improvements throughout the river.

Upcoming work includes:

• Continued remediation and monitoring of contaminated sediments within the Algoma Boat Slip.
• Further evaluation of sediment conditions throughout the Area of Concern.
• A fish telemetry study to track the movement patterns of white suckers and identify where they may be exposed to contaminants.
• Future fish health assessments to determine whether tumour rates decline over time.
• Reassessment of the BUI following additional monitoring.

The planned fish telemetry study is expected to provide important information about whether fish are being exposed to contaminants within the Area of Concern or in other connected waters.