年份,受輕度以下污染河川比率 (%)
1988,77.40
1989,75.17
1990,74.89
1991,75.64
1992,73.93
1993,75.02
1994,75.61
1995,75.68
1996,72.76
1997,74.54
1998,73.62
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
2018,75.03
2019,76.28
2020,77.43
2021,75.67