In those stretches with significantly declining oxygen, there were positive
correlations between DO and TON, BOD and SRP. In stretches with no significant change (or an increase) in DO, significant positive correlations with DO were
found mainly with BOD, TON, flow and temperature.TON was significantly associated with DO in all rivers except the Deben and Waveney. Chloride was important in all rivers except the Blackwater, while BOD was correlated positively with DO in all rivers except the Waveney.