The impacts of combined sewer overflows and surface water outfalls on receiving water quality are assessed by comparing dry weather flow and storm event concentrations of dissolved oxygen, BOD, total and unionised ammonia, pH, dissolved copper and total zinc with those recommended by the River Ecosystem classification guidelines for freshwaters in the UK. The deteriorating conditions during wet weather are identified by water quality falling below the RE2 category for all monitored pollutants, other than dissolved copper, and reaching the most grossly polluted condition for BOD and total ammonia.

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