For centuries, people have looked out at the Mississippi River flowing past Vicksburg and used the word “powerful” in their descriptions.

All of them were correct.

Millions of gallons of water flowing downhill at a speed of a few miles per hour create a strong, steady, natural force.

But for some reason — perhaps because oil and gas have been so cheap for so long and the engineering has been complicated — harnessing the force or tapping a fraction of it has not seriously been contemplated.

That’s changed.

Robert Crear of Vicksburg is leading the efforts of Free Flow Power Development Company of Massachusetts to install turbines below navigable depths at 55 sites along the lower river. Two sites are near Vicksburg and an informational session was held here last week.

Crear brings the resume of resumes to the job.

A retired brigadier general, he is the immediate past president of the Mississippi River Commission and commander of the U.S. Army Corps of Engineers Mississippi Valley Division. In those roles he was responsible for navigation and flood control works along the river and its tributaries from Canada to the Gulf of Mexico.

He’s also a “local,” having graduated from Rosa A. Temple High School and Jackson State University before beginning his military service that also included removing the water from New Orleans after Katrina and putting out oil well fires after the invasion of Iraq.

Around town, he rides a Harley that stands out among Harleys, engages in a lot of philanthropy and community work and says, “hoo-ah” a lot.

As a personal note, two years ago I was in a group visiting Old River Control Structure, the Corps complex designed to perform the not-so-simple task of keeping the Mississippi from rerouting itself into the Atchafalaya River basin. Crear was intently studying a diorama and listening to an explanation of how the fairly new Sydney A. Murray plant is working at Old River. It’s Louisiana’s first and only hydroelectric generator, using a 15-foot differential between the two rivers to spin turbines and power the town of Vidalia.

Turbines planned by Free Flow are a different design, but all do the same thing a windmill does. Blades capture moving elements, air or water or, in the case of steam, both, and through a series of cogs and gears spin a generator. One form of power is converted to another form of power.

Much of the credit for the new enthusiasm for seeing river and ocean currents as underwater windpower goes to Dr. Alexander Gorlov, a mechnical engineer at Northeastern University in Boston. About 10 years ago he began publishing preliminary designs and calculations showing that, among other things, the Amazon could easily produce enough electricity for every city along its course.

Moving from the drawing board to an operational level won’t be easy. Monetary and regulatory challenges loom large. Politics, too.

Free Flow estimates $3 billion as the cost for its 55 sites and, besides, somebody’s already selling electricity everywhere the company would expect to find customers.

For instance, if the state of Mississippi has “certificated” Entergy to sell all the electricity in this region, would Entergy have to buy from Free Flow? Or if Entergy didn’t need the power, would the company be required to allow Free Flow to use Entergy’s grid to sell to others?

Free Flow hopes to apply for its final license from the Federal Energy Regulatory Commission in 2012 and get started in 2013.

Lots of water — powerful water — will pass under the bridges here before then.

It’s neat, though, that the Mississippi’s potential is being seen in this new way. And imagine utility bills with no “fuel cost adjustment” because the fuel is free and the supply is endless.