Immediate response of fish communities and water chemistry to causeway breaching and bridge installation in the Kaouk River estuary,British Columbia,Canada

The Kaouk River estuary is located on the northwest coast of Vancouver Island, British Columbia, Canada, in the Treaty Settlement Lands of the Ka:'yu:'k't'h'/Che:k'tles7et'h First Nations. Stretching across the widest point of this estuary is a causeway providing road access to Fair Harbour. This causeway was observed to decrease habitat connectivity throughout the estuary, specifically limiting juvenile salmon access to high‐quality rearing habitat in the tidal marsh. As such, the causeway was breached in 2019 and a bridge was installed. Juvenile salmon were observed using the new connection and were captured both up and downstream of the causeway immediately following breaching. Postbreach water chemistry (dissolved oxygen, pH, salinity, and temperature) near the causeway was recorded within the range of values observed throughout the estuary. Use of the breach by juvenile salmon and homogenized water chemistry indicate the project succeeded in improving habitat connectivity within the Kaouk River estuary and has enhanced juvenile salmon access to 2.7 km² of wetland rearing habitat.