Statistics
Year 1986 1991 1996 1997 1998 1999 2000 2001
% 58.30 58.30 41.70 41.70 33.30 33.33 25 33.33
Year 2002 2003 2004 2005 2006 2007 2008 2009
% 33.33 25 33.33 33.33 33.33 16.67 16.67 16.67
Year 2010 2011 2012 2013 2014 2015 2016 2017
% 16.67 16.67 16.67 8.33 16.67 16.67 16.67 16.67
Year 2018
% 16.67

Operational Definitions

The percentage of major rivers and streams that are classified as bad or very bad. The rivers and streams referred to include: Ho Chung River, Kam Tin River, Lam Tsuen River, Mui Wo River, River Beas, River Ganges, River Indus, Sam Dip Tam Stream, Shing Mun River, Tai Po River, Tuen Mun River and Yuen Long Creek. The quality of these rivers are measured by the Water Quality Index compiled by the Environmental Protection Department. Water Quality Index refers to annual average index of the stream sampled at a specific location based on measurements of dissolved oxygen, 5-day biochemical oxygen demand and anmoniacal nitrogen. Rivers with water quality indices of 3.0-4.5 are classified as of excellent quality, 4.6-7.5 as good, 7.6-10.5 as fair, 10.6-13.5 as bad and 13.6-15.0 as very bad.

Footnote

All figures are collected from Census and Statistics Department since 1986.
Figure for 1988 is used as a proxy for 1986. Figures for years before 1998 are not available.
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