sentences:  However, an investigation shows that 19 per cent of water in main rivers which has been polluted as well as a total length of 95,000 kilometers.In addition, a survey for 878 rivers in the early 1980s shows that 80 per cent of them were polluted to some extent, and fish became extinct in more than 5 per cent of total river length throughout the country.Furthermore, there are over 20 waterways unsuitable for agricultural irrigation due to water pollution.