Indian rivers are classified as major, medium and minor rivers depending upon the basin area. The information from bio-mapping helps in the classification of zoning of water bodies according to the level of ecological degradation. To indicate the water quality of an entire river basin, maps are drawn based on bio-monitoring and the action plan for pollution control is prepared by simple comparison of the colour maps of water quality of previous years. The typical example of water quality mapping of rivers at North - Rhine - Westphalia, Germany is depicted in Map I and II.

  

Bio-mapping is the technique of transformation of biological water quality information of a river basin in the form of a colour map. Different colours on a river basin map, such as blue, light blue, green, orange and red, indicate various water quality classes in terms of clean, slight pollution, moderate pollution, heavy pollution and severe pollution of a water body respectively.

Monitoring of Rivers

The river water quality monitoring is most essential aspect of restoring the water quality. The Central Pollution Control Board (CPCB) has a nation-wide responsibility of water quality monitoring and management of rivers. The existing water quality monitoring network in India includes 495 monitoring stations located in various water bodies all over the country. The water quality at these stations is monitored through three major schemes such as;

i) Global Environmental Monitoring System (GEMS) - 50 monitoring stations are operated.

ii) Monitoring of Indian National Aquatic Resources (MINARS) - 480 monitoring stations are operated.

iii) Yamuna Action Plan (YAP) - 15 monitoring stations are operated.

All these monitoring stations are distributed on various natural aquatic resources. In all 165 stations are located on major, medium and small rivers, 185 stations on tributaries and 71 stations are located on independent rivers. Other than rivers, the water quality network also covers the water quality monitoring of lakes on 35 locations, ground water sources at 24 monitoring locations and 16 monitoring locations on other sources. The entire water quality monitoring is performed through State Pollution Control Boards, and CPCB zonal offices. At present the water quality monitoring is undertaken for 23 physico-chemical parameters at monthly/quarterly interval.