I heard about similar methods decades ago in Germany. It was some species of fish, which are very sensitive to pollutants. Especially in the old days, before we had high tech sensors, this was a very valuable method to control the water quality.<br>Using animals as sensors is a very old procedure - we all have heard of the canary in the coal mine. Thats just the same kind of method to detect danger.,(reply>), Probably trout.,(reply>), Oh, thank you for the reminder of the famous canaries!,(reply>), it's still being used,(reply>), There was (is?) a bio watch system with fish in a cooperation between Germany and The Netherlands at the Rhine with a prepared ship which had fish onboard to monitor the pollution of the Rhine. It wasn't for drinking water but pollution in common. Of course, alarms were sent to drinking water companies with intake of the river is pollution was found.