(i) Benthic macro-invertebrates are the best suitable biological parameter, among the biotic communities in aquatic ecosystem, for bio-mapping of water body.

(ii) Locations on a river basin map are selected for biological sampling.

(iii) Biological sampling is undertaken at a water depth of less than one meter, with the help of hand net, hand picking, uprooting the plants, shovel etc. and by Eckman grab and artificial substratum at a depth of more than one meter depth.

(iv) Taxonomic identifications of benthic macro-invertebrates upto family level.

(v) Biological water quality evaluation through:

(vi) Assigning the water quality class, to each sampling locations, with respect to combinations of saprobity and diversity score of the biological sample using Biological Water Quality Criteria (BWQC).

(vii) Translating the biological water quality class of each location on river basin map into respective colours assigned in Biological Water Quality Criteria (BWQC).

(viii) Preparation of the coloured Bio-map of entire river basin for identification of pollution control strategies rationally.

Under the Indo-Dutch project on development of Bio-monitoring methodology, emphasis has been laid for adoption of following methods for biological water quality evaluation. These methods are complementary to each other for biological water quality evaluation.

This methodology the involves inventory of the presence of benthic macro-invertebrate fauna up to the family level with taxonomic precision. All possible families having saprobic indicator value are classified on a score-scale of 1 to 10 according to their preference for saprobic water quality. The saprobic scores of all the families are registered and averaged to produce BMWP score.

The methodology involves pairwise comparison of sequentially encountered individuals and the difference of two benthic animals can be observed up to the species level, where no taxonomic skill is required. The diversity is the ratio of the total number of different animals (runs) and the total number of organisms encountered. The ratio of diversity has a value between 0 and 1.

Normally, high diversity of benthic animals always support a good quality of water. However, diversity alone can not indicate the overall health of water body. High and low diversity could be of tolerant, or sensitive animals to pollution. For biological water quality evaluation the diversity of benthic animals is compared with the saprobic score with the help of Biological Water Quality Criteria (BWQC).