The presence of an organism can be used as an indicator of water quality. Scientists in New Zealand have devised a scale from 1 to 10 to indicate an organism’s sensitivity to water quality. On the scale, 1 equates to a high tolerance of pollution (very poor water). At the other end, 10 equates to a high sensitivity to pollution (pristine water). Midge larvae (Chironomus species) are at 1 on the scale: they tolerate a range of conditions including very poor water quality.
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Photograph by Stephen Moore
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