- It is important to have some idea of the freshwater macroinvertebrates likely to be present in good, clear water in your area. A list (e.g. Worksheet “Pollution detectives in rivers”) can be prepared with the animals most susceptible to organic pollution at the top and those most tolerant of pollution at the bottom.
- Take lists of animals found in each sample (from Lesson 3.1). Sort animals and record the presence or absence of each animal or type of animal from the Worksheet “Pollution detectives in rivers” or from the worksheet that was specially prepared for your site.
- Take the Worksheet “Water quality analysis” and fill in the counting results. The greater the diversity, the better the water quality. Also, the higher the score, (the more of the type towards the top of the list) the better.
- To make the assessment more realistic, you should take into account the relative abundance of each animal or group, scoring each into a broad category (such as: 1 = one individual animal from a particular species only; 2 = between 2 and 10 animals; 3 = between 11 and 50 animals; 4 = between 51 and 100 animals; 5 = over 100 animals found in the sample). Help yourself with Worksheet ‘Water quality analysis’ to get a final (or total) score.
- Go to other locations and take new samples. It is important to use exactly the same technique of sampling at each site to compare the results. Remember to compare “like with like” so that a fast stony section can be fairly compared with another fast stony section of a river, and a slow, muddy section with another slow, muddy section of a river since the animals will differ.
Activity adapted from Environmental Education Activities for Primary Schools – Suggestions for Making and Using Low Cost Equipment – Environmental Education Series 21. UNESCO International Center for Conservation Education, Cheltenham, 1992, Chapter 4 Water, Activity 4.9. Pollution detectives, p.61 – 63.