You can’t tell how polluted water is by just looking at it. But by examining the types of species living on the water, you can get a good idea of how polluted it is. Many creatures live in water sources like lakes, rivers, ponds, and streams. Not all animals can live in polluted waters, where they live depends on how much-dissolved oxygen is present in water. There are many indicator invertebrate animals, that are particularly sensitive to a specific environment.
Based on the following 5 creatures you can figure out how polluted the water is.
1. Stonefly Nymph
Stonefly Nymph prefers to live in fast-moving water in amongst the gravel and stones. It requires high oxygen levels and cannot survive in places with anything more than a trace of pollution. They are usually herbivores or detritivores, feeding on fresh or decaying vegetation. Later in their life cycles, many become omnivorous or even carnivorous.
2. Mayfly Nymph
Mayfly Nymph cannot tolerate any pollution and needs water with high oxygen levels. It also feeds on fresh or decaying vegetation, though some larger species are carnivorous. It prefers shallow cool water such as the edges of lakes and streams and burrows into the sediment.
3. Freshwater Shrimp
The freshwater shrimp also likes high levels of oxygen. They likes fast flowing water with pondweed growing on the rocks and stream bed, but it can tolerate some pollution. Freshwater shrimps feed on fresh or decaying vegetation, including fungi and algae.
4. Water Louse
If you discover water lice living in the pond or stream, then the water is moderately polluted. These are related to woodlice and live and feed on decaying materials on the bottom.
5. Rat-Tailed Maggot
Rat-Tailed Maggot is equipped with a breathing tube through which it can obtain the oxygen it needs to survive. This maggot feeds on decaying matter in highly polluted or stagnant water with low oxygen levels.
Source – Wikipedia.org