Dissolved Oxygen Monitoring in Proximity to Large Rafts of Invasive Water Hyacinth Eichhornia crassipes and Its Potential Impacts to Chinook Salmon Oncorhynchus tshawytscha Migration Timing in the Lower Tuolumne River, California

HDR Engineering Inc. along with the Turlock and Modesto irrigation districts conducted an investigation to measure dissolved oxygen (DO) concentrations in proximity to large rafts of water hyacinth (Eichhornia crassipes) along the lower Tuolumne River. Three sites were selected based on the presence, size and density of a water hyacinth raft. Onset™ Hobo DO loggers were placed both upstream and downstream of water hyacinth rafts in order to monitor the effect on dissolved oxygen levels within the water column.  Loggers were placed at sites in September of 2014 and set to record temperature (^oF) and DO (mg/L) at hourly intervals.  Diurnal fluctuations in dissolved oxygen were observed at each of the three monitoring sites.  Adult Chinook salmon (Oncorhynchus tshawytscha) weir passage timing was then examined in the context of DO levels at monitoring sites.