For three decades or so, along the populated waterfronts of California's coastal cities and in many other metropolitan areas situated on the water, every little spot was exploited. Bars, restaurants, hotels hugged the scenic waterfront, sometimes only a few feet of it, and collected big returns.

But along Boston Harbor, well into the '90s, there are vast wasted areas of waterfront - areas that once were busy with industrial or maritime uses but have sat decaying for years since the businesses moved out.

Now, at last, the recognition has hit that this is limited and priceless real estate. And along with the rush to build along the water - as seen recently in Charlestown, downtown Boston, and along Old Northern Avenue in South Boston - has come interest in getting there by water.

``We think this is an area people will commute to,'' state transportation secretary Patrick J. Moynihan says of the new frontier along South Boston's Seaport area. ``It certainly lends itself to water transportation.''

Though some of the routes have been a little late in getting onto the waves, the Big Dig jump-started water transportation. In return for its environmental permits, the project promised to provide water shuttles to help people get to work while the streets were torn up. So, as of last summer, there were a few opportunities to take a boat to work or for a day of recreation - more, at least, than there were in recent Boston history.

A pilot program for a Salem-to-Boston ferry began in July and was initially so successful that it seems to have a good chance of being picked up by a private operator. It could join the Hingham-to-Boston boat, whose riders are fiercely loyal, as a year-round staple.

Astrid Glynn, a policy maker at the Massachusetts Highway Department, says the shuttle from Lovejoy Wharf near North Station to the World Trade Center will soon include a stop at the new dock being built as part of the federal courthouse development at Fan Pier.

``A lot of this will be by demand,'' says Glynn, and the Salem ferry showed that the demand exists. The state transportation office has $50 million to spend over the next several years on programs to test routes that later could turn into permanent commuter services.

An East Boston shuttle was shut down last year for lack of interest, but transportation insiders say its location had been chosen as a political favor and was simply inconvenient. A new location could mean a successful East Boston link in the future, and the Logan dock already serves airport passengers from both Rowes Wharf and Quincy, as well as being used by the unsinkable Boston Water Taxi, the harbor's seasonal on-call service.

The most recent water transportation study recommended adding a stop at the Marine Industrial Park in South Boston by 2010. And a new on-and-off spot is being constructed by the MBTA at Russia Wharf on Fort Point Channel, a belated piece of Big Dig construction ``mitigation'' that won't be ready till 2001.

Unfortunately, the Congress Street Bridge is an impediment to bringing a shuttle boat farther down the Fort Point Channel - to South Station, for example, where thousands of train riders could make connections. But the boats that can go underneath the bridge don't meet stringent federal public transportation requirements for riders with disabilities, so no service is planned.

But where there's a will .... The determined owner of the Boston Water Taxi, Rob McPhersoncq, has demonstrated that he can squeeze a vessel under even the low, low Summer Street Bridge. He had to lower the canvas top (the demonstration run took place in summertime), and passengers had to duck. But he got them to South Station.

Someday commuters will no doubt wave at each other on boats crisscrossing the harbor in the midst of rush hour. And the traffic jams should be more bearable. After all, unlike trains and cars, boats can sail any open space to their destinations, not just where the road is paved or the tracks extend.

Perhaps SmarTraveler, the phone and on-line transportation information service, will have a number to push for the status of water shuttles. Or maybe it won't be necessary, because they'll always be on time.

-- THOMAS C. PALMER JR.