Mollusc specialist André Martel of the Canadian Museum of Nature explains that the freshwater clams of North America (also called freshwater mussels) are bivalves belonging to the superfamily Unionacea. Many different species inhabit Ontario's lakes and rivers and were eaten for centuries by First Nations peoples, particularly when game was scarce. No doubt the early Europeans also learned to appreciate them when times were tough. They're not normally anyone's first food choice, explains Martel, because their flavour can be iffy. "It's not like eating a nice big bowl of PEI marine mussels," he says. "They tend to taste like whatever bottom they came from."

Back when our ancestors were using them for survival food, however, there was no pollution to speak of. The real problem with eating freshwater mussels these days is that they are "filter feeders," constantly ingesting the water around them, filtering out whatever is in it, and bioaccumulating a variety of substances, including pollutants and toxins, in their own tissues. Mussels can live for years - some species for decades - and even distant sources of pollution can produce high levels of toxins. They may also feed on organisms that produce toxins of their own, so eating mussels even from water without evident pollution could be problematic.

Unfortunately, Martel says, freshwater mussels are on the decline all over the world, from pollution, habitat destruction, and the decline of the fish species that serve as hosts for their larvae. Since new species go on the endangered list every year, he discourages collecting them at all.