,受輕度以下污染河川比率 (%)
1999,73.81%
2000,75.61%
2001,71.46%
2002,74.45%
2003,72.86%
2004,73.85%
2005,74.12%
2006,74.51%
2007,69.70%
2008,74.21%
2009,75.25%
2010,69.94%
2011,73.67%
2012,72.41%
2013,70.10%
2014,72.12%
2015,74.84%
2016,73.96%
2017,78.42%