The line chart shows the proportion of river water in the UK that was classified as having good chemical quality between 1990 and 2002.
Overall, Wales and Northern Ireland consistently recorded the highest levels of good-quality water, while England and Scotland showed much greater fluctuations over the period.
In Wales, the percentage remained stable at around 96% until 1998, after which it dropped noticeably to 80% in 2002. Northern Ireland started at about 82% in 1990 and rose steadily to almost 90% by 1996. After a brief dip, it climbed sharply and reached 100% in the final year, becoming the highest among the four regions.
By contrast, the figure for England began at approximately 45% and increased to nearly 70% by 1996. However, it fell dramatically to around 30% in 1998 before recovering slightly to 50% in 2002. Scotland showed a moderate rise from 20% to 30% by 1992, remained stable for several years, and then surged to 50% in 2000. This improvement was short-lived, as the percentage declined again to about 40% in 2002.