Salmonids (which include salmon, trout, char, whitefish and grayling) are very important to the people and ecosystems of British Columbia (BC). While some salmonid populations in BC are healthy, others are showing reduced productivity and/or abundance.

ESSA was engaged by the Pacific Salmon Foundation to conduct an independent review (commissioned by Clean Energy B.C.) of the potential impacts of run-of-river hydroelectric facilities on salmonids, with a focus on facilities currently operating in the province.

With the aid of input from a Public Advisory Committee consisting of academic, First Nations, industry and non-governmental organization (NGO) participants, as well as an Independent Science Panel, we developed a suite of impact pathway hypotheses and a structured methodology to evaluate the evidence for/against each impact pathway.

The impact pathways covered barriers to migration, mortality due to entrainment in the penstock, changes in habitat, alteration of the natural hydrograph, movement of sediment and organic material (primarily wood), changes in food production, stranding due to fluctuation in the wetted width of stream channels, and loss of habitat connectivity.

Scientifically defensible evaluations of impacts to salmonids require extensive monitoring data. Our review relied on information acquired from facility operators (including baseline and operational monitoring data and reports), supplemented with information provided by regulatory agencies, spatial overlays of facility sites and digital maps of fish habitat and fish presence, and an exhaustive review of the relevant literature.

We found that mortality to individual fish (due to entrainment or stranding downstream of a facility) and changes to salmonid habitat (due to changes in flow or movement of sediment and organic matter) were likely or very likely at a number of facilities. However, at the population level, we only found evidence of changes in salmonid abundance attributable to facility operation at one facility (in the diversion reach) and evidence of changes in species composition at one facility (in the upstream reach).

For most of the impact pathways we considered, data limitations prevented us from concluding that impacts were either likely or unlikely, resulting in a conclusion of possible. At 10 of the 23 facilities that provided detailed monitoring information, ongoing monitoring may allow for more complete evaluation of large magnitude changes in resident salmonid abundance (i.e., >50% change) once the first phase (typically five years) of monitoring is complete. Smaller magnitude changes in resident salmonid abundance, or changes in anadromous salmon abundance, are less likely to be detected given current monitoring protocols, except where there is relatively low natural variation in abundance.

Targeted research coupled with the implementation of long-term monitoring protocols at all facilities will be the most effective way to reduce uncertainties related to impacts of run-of-river projects on salmonids.