COLD WATER ON A FATAL CONCEIT? Led by zebra mussels, a host of invasive species is wreaking ecological havoc in Lake Michigan. Some errors are easier to undo than others.

Thanks largely to the Clean Water Act of 1972, it rebounded in the last generation from decades of industrial dumping and, Milwaukee's periodic sewer overflows notwithstanding, its shores are far from the cesspool they were before the arrival of modern sewage treatment.

There are other ecological successes. Scientists used poison to control, but not eliminate, the invasion of lake-trout-killing sea lamprey in the mid-1900s. And shortly thereafter biologists managed an invasion of beach-fouling alewives by planting hundreds of millions of Pacific salmon to eat them.

But that tinkering has perhaps given the public a false confidence in humans' ability to fix the Great Lakes when something goes wrong. Beneath the lakes' shimmering surface, a mounting number of invasive species are wreaking an ecological havoc that scientists are having a hard time understanding, let alone stopping.

Today, at least 180 non-native species lurk in the lakes, and a new one arrives, on average, every eight months. Most come in the ballast water of commercial ships that shuttle between the Great Lakes and Atlantic Ocean via the St. Lawrence Seaway, a largely artificial link between the two aquatic worlds that opened for business in 1959.

Yes, I remember the fireworks show Milwaukee put on to commemorate the opening of the Seaway. International Port of Milwaukee. Big deal. The Seaway has been a net loss to the U.S. and Canada. It is not competitive with deregulated railroads and trucks. And it has been the vector for numerous exotic predators, some of which are doing tremendous damage to the zooplankton of the Great Lakes. (Freshwater lakes with plankton? Yes. One never stops learning. Read the article.)

And don't lose sight of last week's article, spelling out disturbances in the balance of nature that the salmon spawned. (Pun intentional.)

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