During the Northern River Basins Study (NRBS), several issues were highlighted regarding the health of resident fish populations. Based on a basin-wide study of gonad morphology and circulating sex steroid levels, there was preliminary evidence of potential endocrine disruption in fish within the basins. The main concern with this was the potential loss of reproductive capability and possible declining populations. The Northern Rivers Ecosystem Initiative was established in response to the NRBS and an endocrine study was conducted to evaluate in more detail reproductive endocrine function of fish within the identified areas. A suite of endocrine endpoints was used and compared to overall fish health assessments using the Environmental Effects Monitoring (EEM) Programs protocol in areas exposed to sewage and pulp and paper mill effluents. As these northern rivers are nutrient-limited, fish responded to effluent addition (increased nutrients) by showing signs of increased growth and development relative to the upstream reference fish. Some signs of altered reproductive function were observed downstream of the one mill site, however additional responses were observed downstream of a municipal sewage treatment plant discharge from the neighbouring community. The reproductive responses were minimal compared to earlier studies at other older pulp and paper facilities. Follow-up studies at the Grande Prairie site documented changes in the fish responses to the effluents in terms of enrichment. The sewage treatment plant had installed tertiary treatment prior to the latest studies and reductions in the release of nutrients may be the cause. It is not known at the present time whether the pronounced eutrophication response that is still present in these fish may mask other endocrine alterations, as these effluents have endocrine-active compounds in them. The results also emphasize the need for EEM-like monitoring downstream of municipal sewage discharges.

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