The Bridge and Seton watersheds are adjacent watersheds located 200km northeast of Vancouver in the rain shadow of the Southern Coast Mountains. The upper watershed is fed by the Bridge Glacier and primarily influenced by continental and modified maritime weather, with low rainfall in the summer and high snow pack in the winter. Both the Bridge and Seton Rivers flow into the Fraser River near the town of Lillooet.
Salmonid populations in the Bridge Seton Watershed have been affected by dam construction, landslides and harvesting. Dams in the watershed include the La Joie Dam at the Downton Reservoir, the Terzaghi Dam at the Carpenter Reservoir, Seton Dam at Seton Lake and the Cayoosh Dam at Cayoosh Creek.
Salmonids in the Bridge-Seton Watershed
Information on historical abundance and distribution of salmonids in the Bridge River are mostly inferred from historical photos, local knowledge and current fish presence. Most spawning of Chinook, Coho, Steelhead and Sockeye occurred in the middle Bridge River and it’s tributaries. After the Terzaghi Dam was constructed, the lower Bridge became more suitable spawning habitat with chum and pink salmon presently spawning there. Historically, migratory runs of Chinook, coho, sockeye and pink salmon and steelhead trout used the Seton river system. Current resident species of salmonids found in the Bridge River include rainbow trout, bull trout and mountain whitefish and non-salmonids include sucker, lamprey and sculpin.
Impacts
Hydro-electric Related Impacts
Impacts of the hydroelectric dams within the Bridge-Seton watershed include the loss of off-channel and tributary habitat caused by flooding, sedimentation of the Bridge River, reduced downstream flow and reduced recruitment of large woody debris and gravel, which provide spawning habitat to the lower Bridge River. Altered stream flow has also altered the water temperature, which can potentially benefit fish, but also cause temperature stress. Salmon can become trapped by screens and trash racks or be delayed ascending fish ladders. Larger Chinook or Sturgeon cannot use the fish ladder at Seton Dam. Diversion of Bridge River water into the Seton system has significantly altered the water temperature and chemistry. Diversion of the Cayoosh Creek to Seton Lake provides partial migration to Seton Lake and assist Sockeye to Seton River. However the diversion also diminishes habitat, gravel and large woody debris downstream.
Non-hydroelectric Impacts
Mining, forestry, road and rail construction have also affected salmonids in the Bridge-Seton Watershed. Seton and Anderson lakes historically supported substantial runs of sockeye salmon, which were affected by harvesting in the lower Fraser in the 1890s. Two landslides in 1913 and 1914 formed a barrier to upstream fish migration in the Fraser Canyon. Fishways were built and extended in 1945 and 1956 to increase fish movement to the watershed, though stocks took a long time to recover. The effects of the slides are thought to have contributed to the underestimation of the Bridge-Seton fish stocks during the hydro development evaluation in the watershed.
Limiting Factors to Salmonids
- Habitat area has been permanently lost or seasonally reduced
- Habitat quality has been reduced through loss of recruitment of gravel and large woody debris
- Access to habitat has been reduced
- Diversions of water have reduced downstream flow and altered water temperature and chemistry
- Entrapment – it is estimated that 10% of juvenile salmon are trapped at Seton power canal
Habitat Improvement
Changes in BC Hydro operations as part of the 2003 Water Use Plan have improved habitat conditions. Habitat compensation projects have also had a positive impact since 1999. Restoration of habitat by creating in-channel and off-channel habitat, in the lower Bridge river followed by flow release of 3m/s allowed the return of spawning salmon. Complexing of Seton spawning channels, gravel replacement in Gates Creek and Seton River foreshore restoration has also improved salmonids habitat.
Objective of the Fisheries Management of the Bridge-Seton system:
The Salmonid Action Plan has been developed from a strategic framework to guide overall planning and restoration projects for the BC Hydro Fish and Wildlife Compensation Program (FWCP). The action plan aims to:
- Ensure diverse and productive ecosystem
- Improve species of conservation concern status in the watershed
- Promote sustainable use
Future Work
Knowledge gaps have been identified and are to be addressed by the Salmonid action plan. These include information on habitat limitation and habitat restoration opportunities, methods and feasibility. Monitoring of previous restoration efforts is also a priority.