EVEN THOSE OF us who live right next to them tend to forget just how important the Great Lakes are. Perhaps, as William Ashworth points out in this fine study of what has happened, is happening, and may yet happen to the lakes, part of the problem is their name.

Superior, Michigan, Huron, Erie, and Ontario are officially lakes, and it's easy to think of a lake as something we can get around to saving later on. Ashworth disabuses us of this notion in his first sentence: "There is a fifth coast of North America, one that lies not at the edge like the other four . . . but at the center, along the midcontinental line. . . . In no conventional sense are these lakes." And he quotes Larry Chitwood, a geologist with whom he did some of his exploring, as saying, "If we called them seas, it might be easier to protect them. What's the significance of losing a lake? If you lose a sea, you're losing something important."

The Great Lakes are certainly oceanic in their strength, temperament, and all-round presence. They have tides and surf. They are big enough to contain fish species that normally spend most of their lives in salt water and enter freshwater rivers only to spawn. They have seiches, which are tidelike motions caused by differences in barometric pressure that can rock for days from lake-end to lake-end, "like water sloshing in a bathtub."

More ships, carrying more tonnage, traverse the locks at Sault Ste. Marie, where Superior and Huron Meet, than use the Panama and Suez Canals combined. Twenty-four million people get their drinking water from the lakes. And, perhaps most amazing, salt is mined even today in downtown Detroit and in Cleveland. It was deposited there a few hundred million years ago when the lakes were connected to the Atlantic.

The author is less forthcoming about providing us with the lakes' fundamental statistics. Numbers can be deadly in a book like this, but a serious volume dedicated to explaining the Great Lakes should contain at least a handful of World Almanac-type statistics. Ashworth does refer to the Great Lakes' coastline's "nearly 10,000-mile length," and some facts are included in charts and tables, but even more wouldn't hurt this book.

Ashworth organizes his material into a roughly chronological account of the things people have done to the lakes since the Europeans "discovered" them. First came the fashion among white men of wearing hats made out of beavers. The second step involved the wholesale destruction of forests, known as the Big Cut. Then came the extraction of minerals -- iron, copper, limestone, sandstone, nickel. All the generations of exploitation have depended on waterborne transportation. That, in turn, has created another pressure on the lakes, as engineers and bureaucrats dredge, "channelize," move sand around, and erect their interminable (and harmful) groins and jetties. And more recently we have begun to recognize the effects of modern demands on the lakes, chief among them toxic wastes, shoreline development and concomitant erosion, and the introduction through human folly of new and destructive fish species into places where they never lived before.

And that's not all. The latest scheme to damage the Great Lakes, and one that would insure the accuracy of this book's title, is one that Ashworth says "sounds preposterous, and it is, but not because it cannot be done. It can." Politicians and agribusiness interests in the High Plains, having pumped the immense Ogallala Aquifer nearly dry, are now looking toward the Great Lakes. The procedure would be easily recognized by any resident of California or Arizona. Just lay some pipe, dig some channels, and divert the "unused" water from the lakes. IT'S ALL very much in keeping with Ashworth's description of the way exploitation has historically proceeded in the lakes: "Rip out a resource, ship it off for someone else's benefit, and call it development -- and when the inevitable payment came due, rip out something else to raise the cash."

The Late, Great Lakes is a well-written, well-organized book. Although it concerns problems for which a generous amount of collective and individual blame can be handed out, it's not overly preachy. The author, whose most recent book was Nor Any Drop To Drink, an examination of the water situation, reminds us occasionally that it is we who demand the nickel-plated razors, the hard-working detergents, the taxpayer-provided breakwaters, and the beaver hats.

Ashworth writes in a style that is frequently breezy. During the Big Cut, for instance, hemlocks were "felled, stripped of their bark for its tannin, and left to rot where they lay like so many buffalo." Sometimes the breeze approaches a full gale, as when he tells us of "raw hunks of shattered stone that lie over the bank at crazy angles like petrified vomit." But these are minor annoyances.

His message is clear and worthy: The Great Lakes are in terrible danger, and the greatest single source of that danger is not just mining or erosion or toxic rainfall, but the lakes' "ancient enemy," complacency and apathy. It has been far too easy for the people who depend on the lakes, and who should be protecting them, to see their resource as an infinite one. With any luck, this book will help to cure that problem.

But it's going to take a lot of luck. You would think, for example, that the scheme to pipe water from the Great Lakes into Nebraska farmland might so frighten ordinary people and politicians in the Upper Midwest that they would say "Absolutely Not, Never." A few have said No. But Ashworth raises the possibility that the politicians may change their tune if the going price for water rises. This would be an act of transcendent stupidity. One former governor of Michigan is quoted as saying that water "will become for the Midwest what oil was for OPEC," the Organization of Petroleum Exporting Companies. He said that, of course, before the bottom dropped out of OPEC.