First of all, I'd like to point out very quickly that the data we're looking at and the graphs you saw on page 7 actually represent 16 carefully selected sub-drainage basins across the country that are under particular pressure from human activities, from a range of things. Mr. Moffet alluded to those in his presentation.
These actually represent areas where you would expect water quality to be at greater risk. The fact that water quality is improving gradually over time would suggest that prudent water management decisions are being made that are resulting in better water quality over time.
That's the short version of the answer.