A few decades ago the zebra mussels were released in the Great lakes. This is an invasive species, and these small molluscs cause a lot of damage in pipes, especially intake pipes on power plants. BUT after a few years the water clarity improved in Lake Michigan (I live on the shore then). So clams can purify water. THere is not mystery. It's simply what they do.,(reply>), Has this been extensively studied or is this correlation?