The line graph compares the proportion of river water grouped with good chemical quality between four UK rivers from 1990 to 2002.
Overall, it is clear that Northern Ireland experienced the highest percentage of river water despite gradual decline throughout the period, whereas England remained at the bottom of the chart, with the discrepancy between two rivers shortened every two years. Furthermore, Wales witnessed a significant increase, while Ekoksace fluctuated and reached its initial level.
At the beginning of the period, Northern Ireland recorded the highest percentage of good chemical quality, with just above 90%. Although this percentage stayed stable in the early years, it gradually fell afterwards and reached around 80% in 2002. In contrast, Wales showed considerable improvement over the same period. Starting from approximately 50% in 1990, the figure increased steadily year by year and almost caught up with Northern Ireland by the end of the period.
As for the Ekoksace, the proportion of river water with good chemical quality fluctuated throughout the years. It started at about 68% in 1990, peaked at roughly 74% in 1994, and then dropped to around 63% in 1998 before recovering slightly in 2002. England had the lowest percentages among all four countries, despite showing gradual rise. Its figure rose gradually from nearly 23% in 1990 to about 46% at the end of the period.