The opening of the St. Lawrence Seaway in April 1959 was a day of jubilation.

The headline in The New York Times trumpeted that the "Heart of the Continent is Opened to Ocean-Going Ships." The Canadian Broadcasting Corporation told viewers, "A dream is realized." President Eisenhower and Queen Elizabeth II were in attendance. Soon, huge ocean cargo vessels were steaming up and down the Seaway less than 20 miles from Clarkson's campus.

Half a century later, Clarkson biologist Michael Twiss is among a corps of scientists charting the environmental change the Seaway and hydroelectric power projects have wrought. Global commerce for the Great Lakes brought with it scores of invasive species. "A ship coming from the Baltic may carry an uninvited international hitchhiker," says Twiss.

One of those hitchhikers, says Twiss, was the zebra mussel - a small aquatic animal originally found in Russia. The mussel arrived around 1988 and began to breed. Since each female produces one million eggs a year, the burgeoning mussel population has had a drastic effect on the ecology of the Great Lakes.

For instance, the mussels changed the aquatic food supply by filtering phytoplankton, and markedly increased the clarity of Great Lakes water in the process. But the cleansing deprived other species of food. "This caused lake trout to starve," says Twiss, an associate professor of biology and director of the Great Rivers Center at Clarkson University. He said the mussels have also turned some beaches into "middens," or dumps of empty mussel shells.

seawayThe zebra mussel population is controlled in part by the appetite of another species that also arrived via the Seaway - the round goby, a fish native to Eastern Europe's Black and Caspian Seas. The goby showed up in 1990 and began to feast on the mussels. This kept the gobies well fed and helped to control the zebra mussel population, but produced yet another environmental shift. "Things like the sturgeon and the small mouth bass are thriving because they eat the goby," Twiss explains.

It is a case of one thing leading to another, and Twiss wants to better understand how this constantly evolving system works. It is familiar territory; Twiss, a Yankee who grew up on the north shore of Lake Huron in Canada, has been around the Great Lakes all his life. Now he is trying to find out what makes the system tick, with a particular focus on the understudied, 115-mile International Section of the St. Lawrence River which forms part of the boundary between the U.S. and Canada. But Twiss and his research colleagues recognize that the environmental change wrought by invasive species can't be easily reversed.

Rapid ecological change has been a constant in the region since the arrival of European settlers. Since the 1800s, more than 136 invasive fish, algae, invertebrate and plant species have colonized the Great Lakes, according to the U.S. Geological Survey. An early arrival was the sea lamprey, an eel-like primitive fish with a vampire's eating habits. The lamprey hooks its prey with its sucker mouth, drills a hole with its teeth, and then drains its victims of fluids and blood. Its prey includes salmon, lake trout and sturgeon. The lamprey, which was discovered in Lake Ontario in the 1830s, may have entered through the Erie Canal.

But the St. Lawrence Seaway set off a new round of upheaval by allowing foreign invaders to reach the Great Lakes as stowaways in ship ballast, the extra water that ships carry to control stability in the water. When this water was dumped, invaders were set loose. The zebra mussel is believed to have arrived this way. New regulations now control where ballast can be emptied, but they came too late.

The Seaway was built to spur the economies of adjoining states and Canadian provinces by allowing ocean ships to travel unimpeded from the Atlantic to Duluth, Minnesota. It was created by removing roadblocks in the St. Lawrence River, among them the Long Sault Rapids, a 10-mile stretch of white water in the International Section 25 miles from Clarkson. When the Seaway was done, it formed a vast system that included the St. Lawrence River, all five Great Lakes, and adjoining water links such as the Detroit River. The Seaway can now handle vessels roughly two-and-a-half football fields long.

The Seaway changed the region's economy by turning the St. Lawrence into a watery highway for a region of 33 million people. Oil, chemicals, gravel, iron ore, grains and finished products such as wind turbines now move along the waterway. Since its opening, the Seaway has carried some 2.3 billion tons of cargo. The Seaway's key advantage is cost. Big ships use less fuel than trucks or trains to haul cargo, and produce fewer greenhouse gas emissions as well. Future regulations to force ships to use cleaner fuel will make this type of transportation even more favorable.

But when the Seaway's 50th anniversary arrived, the media focused on the undesirable changes it had brought. One of these changes came with the damming of the Long Sault Rapids, which allowed the installation of locks to handle big ships. "They drowned the rapids," says Twiss. This removed the natural fluctuations in water levels, so that cattail marshes took over sections of the river where fish once spawned.

It might seem logical to simply restore fluctuating water levels, and Twiss says several plans to do this have emerged. But Twiss cautions against haste. The danger is that fixing one problem may create another. One sticking point is that wetlands are a natural reservoir for mercury because they aren't flushed by changing water levels. The river has been dammed for half a century and a lot of mercury has accumulated. "It potentially would be released in bulk if the water were allowed to rise and fall more naturally," Twiss says.

It would amount to "yet another disturbance, when we already don't understand fully how things work now," Twiss adds. He is working with colleagues from the University of Ottawa to study the area where the rapids once lay. But even as they work, other changes may be taking place.

"It's like bobsledding," observes Twiss. "You can't get off, and it changes direction so rapidly it is difficult to keep your bearings. For a scientist, it's very challenging. Just when you think you understand the system, something else happens."