LIKE the Great Lakes economy, shipping in the lakes and St. Lawrence Seaway has come back with all the stubborn force of a stone-laden barge churning through a glaze of Lake Superior ice.
Whether hauling potash from Thunder Bay, Ontario to Toledo, Ohio or coal from Superior, Wis. to St. Clair, Mich., vessels in the seaway and lakes are busier today than any time in many years.
Impelled by the nation's fastest growing regional economy, United States ships on the Great Lakes so far this year have transported 12.1 percent more freight than during the same period in 1994. Traffic last year totalled 115 million tons, the highest since 1988, according to the Cleveland-based Lake Carriers' Association.
Tonnage passing through the seaway - which opens the Great Lakes to oceangoing vessels via the St. Lawrence River - has increased 29 percent this year until Aug. 1 compared to the same period in 1994, according to the St. Lawrence Seaway Development Corporation.
The comeback is a boost to about 60,000 workers in Canada and the US employed by the $3 billion shipping industry in the lakes and seaway. It affirms the solidity of waterborne transport after years of decline because of doldrums in the regional economy and harsh competition with railways and other kinds of transportation.
Regional shipping has bounced back largely because of a boom in steel production, say transportation experts.
Shipments of coal, limestone, and iron ore - the primary raw materials in steelmaking - comprise about 80 percent of tonnage shipped by US-flag vessels, says Glen Nekvasil, communications director at the Lake Carriers' Association. (US mills along the Great Lakes produce 7 out of every 10 tons of the nation's steel.)
''If you want to know how Great Lakes shipping is doing, you look at the steel industry,'' Mr. Nekvasil says.
The return of shipping is also good news for the environment of the Great Lakes Basin because ships are cleaner and safer than trucks and trains, according to a 1993 study by the Great Lakes Commission, an agency funded by the eight Great Lakes states.
The commission study plotted several scenarios and determined that in hauling the same amount of freight, trains emit from 47 percent to more than 100 percent more pollution than Great Lakes ships. Moreover, 75 percent of all spills of oil and hazardous waste into the lakes originated on land, according to the commission based in Ann Arbor, Mich.
''The safety and environmental characteristics of waterborne shipping are far better than by rail or highway transportation,'' says Michael Donahue, the commission's executive director.
Some environmentalists note, however, that the shipping industry requires dredging of ports heavily polluted by toxic sediments. Also, ships in the Great Lakes basin sometimes still spill their cargo, and inadvertently carry into the region destructive species like the zebra mussel and lamprey eel. Compared to the oceans, pollution can be especially hazardous in the basin because some 25 million people rely on the lakes for drinking water.
The shipping industry has been buoyed by the comparatively vibrant economy of the Midwest and the rise in demand for transportation because of liberalized global and North American trade.
The General Agreement on Tariffs and Trade ''has given industry in the region a tremendous competitive advantage and raised the overall tonnage we see put through the seaway,'' says Rhonda Worden, a public affairs specialist with the St. Lawrence Seaway Development Corp., under the US Department of Transportation.
In the seaway, rebates on passage fees through two locks controlled by the federal government have also spurred waterborne transport in recent years. The rebates range up to 25 percent, says Ms. Worden, based in Messina, N.Y.
Moreover, shipping companies have successfully recovered business and a measure of public trust by improving their efforts to prevent pollution mishaps following the massive oil spill from the supertanker Exxon Valdez in Alaska in 1989, say the experts.
Most companies have closely adhered to the Oil Pollution Act of 1990, which set up emergency centers to handle spills of oil and hazardous materials, they say. The act also requires the outfitting of vessels with equipment to prevent and clean up spills.
The regional shipping industry will not plow ahead indefinitely. Steelmaking and other cyclical industries along the lakes will eventually falter. Moreover, early or long-lasting ice frequently shortens the nine-month shipping season and compels customers to turn to roads or railways.
For the foreseeable future, however, the Great Lakes shipping industry figures it is unlikely to face the severe boom-and-bust cycle of the past two decades.