BC Estuary Water Quality Monitoring Data - Chemainus River Estuary (Provisional)

Estuaries provide critical habitat for over 80% of BC’s coastal fish and wildlife, including Pacific salmon, marine mammals, and migratory birds. The complex structure and aquatic vegetation of the estuary also serve to filter sediments, sequester carbon dioxide (CO2), and stabilize shorelines from erosion. Anthropogenic stressors from aquaculture, shoreline development, forestry, and pollution can degrade estuarine habitats, impacting spatial coverage and species diversity. In addition to human impacts, climate change is expected to significantly impact estuary ecosystems through several mechanisms, including rising sea-levels, ocean acidification, temperature and salinity changes, and changes to freshwater and sediment inputs. Monitoring these variables through time will provide an effective indication of ecosystem health and productivity, informing decision makers of estuary impacts and resilience to climate change.

From 2019 to 2026, The Nature Trust of British Columbia (NTBC) implemented a monitoring project to assess marsh resilience to sea-level rise. As a part of the monitoring program, NTBC partnered with coastal First Nations to collect detailed water quality data from 20 estuaries on Vancouver Island, the Central Coast, and Haida Gwaii.

Water quality data are collected using an RBR Maestro3 multi-parameter sonde - a multichannel, multi-sensor data logging instrument designed for water column and estuary profiling. The sondes include sensors for conductivity, temperature, and depth (CTD), dissolved oxygen (DO), turbidity (Tu), and photosynthetically active radiation (PAR); certain instruments also include pH (water alkalinity / acidity) sensors. Data are collected during different weather events, tides (flood and ebb), and seasons (spring, summer, fall, and winter) to fully understand the water quality characteristics within the estuaries. These surveys are collected quarterly, with additional surveys collected at some sites during some years, based on staff availability and funding. For the Chemainus estuary, water quality surveys were conducted by Halalt First Nation from July 2023 to present.

Water quality surveys within each estuary were designed to collect cast data along a salinity gradient, from marine to fresh water. Casts were also conducted in locations that may influence water quality in the estuary, including tributaries (freshwater streams that flow into the estuary or the river), urban streams and runoff, and potential sources of effluent (stormwater or wastewater, often from industrial activity).