Think of the Tennessee River as a 652-mile interstate highway.

Imagine the creeks and smaller river tributaries as nearly 350 miles of secondary and community roads.

Now visualize getting from the interstate to your home along those secondary roads without road signs, traffic signals and safety markers.

Making sure the river system's 350 miles of channels are marked and navigable is the job of TVA's service vessel Sideview.

The Tennessee Valley Authority, by the congressional act that created it, is charged with maintaining navigational access on those tributaries that feed the river and help generate electricity.

The U.S. Coast Guard does the same job on the river's main channel - the water interstate.

Carrying out the Sideview's mission costs TVA and ratepayers about $500,000 a year, and this week the boat and its four-man crew are working in one of the nation's busiest recreational boating areas - Chickamauga Lake.

John McCormick, TVA senior vice president of river operations, said the half-million-dollar price tag is far less than what the agency would have to pay if some other federal organization did the work.

"The Corps of Engineers and the Coast Guard estimates were more - in some cases twice as much," McCormick said.

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Sidewinder Capt. Tim Barkley and his crew shook off morning rain Monday and wrangled about a half dozen nearly sunken markers from the channels near the Chickamauga Dam and in Harrison Bay.

They worked in tandem.

Barkley maneuvered the 88-foot, 222-ton boat, using it to both push and pull to position each newly attached "nun" and "can" buoy.

The crew - Chad Gower, Brent Smith and Mike Foster - got wet to hook the red cone-shaped nun markers and green can markers. Then they wrenched them onto the boat where they could cut the steel cables that hold each one to a 150-pound concrete sinker. Then they clamped on a new buoy.

Often the buoys have been cracked when a boat hit them, causing them to take on water and sink. Sometimes they simply have been pulled into deeper water by currents. When that's the case, Barkley uses Sideview's GPS system, sonar and diesel-powered 850-horsepower engine to reposition them.

His is a nerve-racking job as he watches all the instruments, steers and works the boat's forward and reverse throttles to meet the crew's need. They tell by radio and hand signal when they need the boat's help to manipulate the marker.

All the while Barkley must watch his crew and keep the ride smooth enough to keep their footing steady.

But there is a perk for his position.

"I'm always in the air conditioning, and I stay dry," he said with a smile.

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Chickamauga Lake has the highest recreational boat traffic on the Tennessee River, and the fifth-highest in the country.

About 5,000 recreational boats use Chickamauga, said Lana Bean, TVA's navigation program manager.

Every one of those boats must motor or sail some of the tributary creeks and bay channels to get in and out of their marina or boat launch.

At Harrison Bay, a missed channel can mean an encounter with an unforgiving rock. Similar dangers lurk in all the tributaries and around the marinas that populate them.

Boaters there use the buoy and navigational systems much as vehicles on secondary streets use lane markers, road signs, traffic signals and mile markers.

Twice a year, the Sideview travels the entire Tennessee River and its tributary channels. The crew works four 10-hour days a week, and each year they log about 4,000 miles of water.

Along the way, they maintain more than 2,000 navigation aids, including buoys, daymarks, daybeacons and fingerboards that mark the secondary channels.

They eat and sleep on the boat, which has a galley, four 8x8 staterooms, two full baths, a half bath, a conference-media room with four recliners, an exercise area and a large pilot house.

They travel with one vehicle on the derrick barge at the front of the boat so they can drive home to the Florence/Muscle Shoals area of Alabama each weekend.

The derrick barge also holds a smaller creek boat, a lifeboat, a supply of buoys and other navigational aids, sinkers and two cranes for positioning all those supplies.

Named for the hometown of former TVA board member Johnny Hayes, the Sideview was commissioned in 1996. The $1.5 million boat replaced a previous TVA service boat named Pellissippi, which had served the same purpose from 1948 until 1996.

Crew members say being away from their families for four days a week is tough.

But there is an upside, according to Brent Smith.

"Look at our office. Look at what we wake up and look at every morning," he said with a nod toward the river, shining silver in the day's gentle rain.