Asian clams' spread in Columbia River warns of worse invaders

The invasive Asian clam is more common in the lower Columbia River than its native habitat of southeast Asia, according to a study of the clam's abundance in the river. The findings don't bode well for potential future invasions by the even more destructive quagga and zebra mussels. So far, the Columbia is one of the only major U.S. rivers to remain free of these notorious ecology-destroying, equipment-clogging bivalves.