Finally, I read the Dive Training magazine and it confused me and I hope that someone would be able to explain it to me.
The article about the zebra mussels in Millbrook on page 20 says:
the mussels have spread through the Great Lakes and major rivers, killing marine life, clogging drinking water intakes and costing billions of dollars to control.
I have no problem with that, but in the same magazine and in the same issue on page 95 an article about Portage Quarry Recreation Club says:
The lake supports a significant population of freshwater fish, including largemouth and smallmouth bass, bluegill, carp, northern pike, walleye, channel catfish and yellow bullhead. Crayfish, turtles and zebra mussels can also be spotted.
The proliferation of zebra mussels, which has seriously damaged some ecosystems, has thus far benefited Portage by improving the visibility.
I feel that they have two faces, the first article stating that the mussels are too bad for the environment and for our daily life, but in the second one, they are bad for some ecosystems.
Could anyone explain it to me?