The data used were for the period July–September (summer) because it was in these months that RE targets generally failed due to low DO. Summer means were obtained for environmental variables that may have influenced DO, whether directly, or indirectly through effects on vegetation or sediment. These determinants were SRP, biochemical oxygen demand (BOD), total oxidized nitrogen (TON), ammonia and chloride. Temperature and flow were also used. Although the full data set could not be tested for validity, we analysed water samples collected in the Rivers Brett and Deben over two summers and compared the results with those obtained from the same rivers by the
Environment Agency. Both sets of results were found to be similar.