On Wed, 15 Jul 2009 21:37:20 -0700, Tim wrote:

Could they become a new fresh water plague?

Not that I would suggest tampering with an ecosystem, but Zebra Mussels
are not without some positive aspects. Their filtering capabilities can
improve water quality and clarity. There are reports of areas where the
smallmouth, perch, and even salmon fishing has improved after Zebra
Mussel infestations.

http://seapics.com/feature-subject/m.../zebra-mussel-
pictures.html