We measured dissolved O 2 concentrations, p CO 2 values, and respiratory rates in five estuaries of the southeastern U.S. in October 1995 and July 1996. In the low‐salinity sections of the coastal plain rivers, dissolved O 2 saturation states were typically only 50%, while p CO 2 values were over 4,000 matm. Respiratory rates measured concurrently in estuarine water averaged 8 and 23 mmol m −3 d −1 in October 1995 and July 199...