Measurements are made using a YSI 6600 water quality datalogging sonde. YSI Sonde sensors consist of 6150 optical dissolved oxygen probe , 6560 conductivity/temperature probe (thermistor) and vented level depth sensor (stainless steel strain gauge). Missing data or blank values are caused by maintenance time periods or where sensor measurements are obviously wrong in the context of what would be expected. For example, the conductivity sensor has a relatively small opening and chamber for the conductivity electrodes, the estuary can have varying suspended sediment/detrital loads moving in the water column which enter the conductivity cell shorting out the electrodes making a faulty conductivity measurement (lower than expected). Oxygen measurements are dependent upon the conductivity measurements so the oxygen also becomes erroneous. Obvious measurements/data errors have been removed from the data set however the user of this data should also conduct their own data analysis to determine if the data are suitable for their particular situation. Typical sensor/data problems are: For oxygen: Poor/inaccurate conductivity measurements will affect the dissolved oxygen accuracy For conductivity: Conductivity cell can have detrital material stuck in it, shorting out cell, resulting in lower than expected conductivity. For depth: Depth strain gage pressure sensor may come out of the water at low tides resulting in many "zero" depth readings or sometimes negative values. YSI Dissolved oxygen % saturation reporting can vary depending upon how the oxygen is calibrated. For this data set two Oxygen percent saturation values are reported. ODO%YSI variable name represents a YSI calibration in air, from Standard Methods, refers to calibration at a particular ATM pressure which allows DO% for calibration to fluctuate above/below 100% when ATM is above/below reference 760 or 1 ATM ODO%Local variable name represents an oxygen calibration in air at a particular ATM pressure but it forces the DO% to be 100%, does not allow it to be under or above if ATM is above/below 760. ODO%Local data should be used for metabolism studies when correcting for diffusion based on gradient deviations from 100% which by definition is the % saturation of oxygen in air. ODO%YSI should not be used since it would require a known ATM pressure at each interval to calculate the ATM % saturation of oxygen to be use for that interval, probably a small correction anyway. Concentration of DO remains the same for either calibration. A Campbell CR1000 is logging the data and we use radio telemetry to a base station in Rowley for streaming the data and downloading to a computer.