Fish Health and Pulp and Paper Mill Effluents: Findings from a Multi-Year Study

The Long-Term Receiving Water Study (LTRWS) is a multi-year year study examining the influence of pulp and paper mill effluent on four receiving water stream ecosystems (Codorus Creek [PA], the Leaf River [MS], and the McKenzie and Willamette Rivers [OR]). Sentinel fish populations were examined to determine spatial and temporal patterns in Condition Factor (K) and percent deformities, fin erosion, lesions and tumors (%DELT).

Overall, the response of fish K and %DELT to pulp and paper mill effluent exposure was minimal. In all rivers, K showed few clear spatial trends and no apparent impact from effluent exposure on selected fish species. Patterns of %DELT were unrelated to effluent exposure in most streams. In Codorus Creek, there was high %DELT immediately downstream of the effluent discharge which decreased with increasing distance downstream. However, one upstream site showed a similar %DELT indicating that other watershed factors may have been contributing to the pattern displayed by this metric. In all streams, both endpoints were temporally variable across years, with seasonal differences seen in some streams.

The results of this assessment indicate that there is very little evidence of effluent-driven reduction in the health of selected fish species in the LTRWS rivers. These findings likely reflect high effluent quality and are consistent with the responses of other in-stream biota and laboratory assessments. The strength of these results lies in the spatial extent of study reaches, and the multi-season and multi-year dataset on which findings are based.