The Podolí water treatment plant in Prague, Czech Republic also uses biomonitoring. But instead of clams they use trout. The trout are on the intake side of the plant right after the stage where water is combed for large mechanical contaminants (think trash, floating pieces of wood, leaves etc.) before any fine particle filtering or chemical treatments to maximize the chance that any toxic contamination would be detected. Sensors and lab tests which are obviously the main method of detection only detect stuff that you are specifically testing for, they do not work for unique and unforseen threats. On the other hand a living organism doesnt have to know what it is being poisoned by to get poisoned.