The river's C behind them, the Columbia bent south and began a wide turn back west. The Yakima River came in from the right. At the Tri-Cities of Richland, Kennewick and Pasco, the Columbia became a reservoir again and was joined by the Snake River.

In a park at the river-junction stood a monument to Sacajawea, Lewis and Clark's Shoshone Indian guide. Lewis and Clark had come over the Rockies and down the Snake exploring the Northwest wilderness for young America.

The modern river here became a highway of commerce. Huge tugs nosed barges up and down the reservoir, in  to and out of the Snake River. Leslie was reminded of those social studies maps with their little sheaths of grain, oil derricks, cattle. The Columbia was a river of moving products.

"l used to shove these barges all the way to Lewiston, Idaho," said LaFont. "The Snake, the Columbia's largest tributary, is a big work-horse these days."

On its way from the Grand Tetons in the Wyoming Rockies, the Snake irrigates a wide swath of southern Idaho. It is the lifeblood of most of the state's population, and for Idaho's famous potatoes. Dworshak Dam, on the Snake's Clearwater River tributary, is an important storage dam. Dams on the lower Snake make barge traffic possible while they spin out electric power.

Of all the Columbia's main tributaries, LaFont said, the Snake River has the most pressure on its water supply. Competing uses of the Snake - for power, irrigation, navigation and fish - keep people arguing about how to use the river.  It was August. Leslie began consulting the map and counting the days left before school. Would they make it all the way to the Pacific? A grain barge idled before the lock at McNary Dam. LaFont pointed his paddle at the tug boat. He shouted at the captain. "Shuv Nordquist!" he bellowed.

The weathered captain, wearing a Seattle Mariners cap, did a double-take as he recognized his old tugmaster friend. "LaFont!" he shouted back.   The captain climbed down from the bridge and dropped a short ladder over the side of the tug. Leslie climbed on board. Her grandfather and the captain whacked and hugged one another. LaFont did the introductions. "When push comes to shove," he said, "Shuv comes to push. Is that right, Shuv? Shuv Nordquist, this here's my granddaughter, Leslie."

Shuv ordered a crew guy to hoist the canoe aboard the tug. "We'll carry you through the lock," he said. You two look about beat."

Shuv demanded that they stay on the tug for dinner. They had thick T-bone steaks and baked potatoes in the galley. The two men talked. Shuv Nordquist was riled up about how the Snake River was silting. In spite of regular dredging, it was getting dangerous for barges below Little Goose Dam. "They'll either have to dredge deeper or release more water," he said.

"There's always something," said LaFont. "As much as this river does, people always want more."

Leslie noticed the tug's bunk beds. When Shuv invited them to stay the night , she caught her grandfather's eye and gave him a nod.

"I guess it wouldn't hurt if we didn't paddle every inch of this river," said LaFont. "We're still on it." John Day Dam was a pause in the night, unnoticed by Leslie as she slept. The next day, when she awoke, they were gliding between brown-baked hills. The Columbia formed the border between the state of Washington, on the right, and Oregon.

They passed the site of the famous Indian fishing village of Celilo Falls. Like Kettle Falls, Celilo was once a major gathering and trading place for Northwest Indians. Salmon caught at the falls were the Indians' food, their currency, and a big part in their religion. Now Celilo Falls is under water. A park and a boat launch mark the spot, next to the flat reservoir.

"This used to be a nasty set of rapids," said LaFont. "Wagons on the Oregon Trail," he said, "got to Celilo and had to make a choice. Some took the Barlow Trail - around Mt. Hood and into the Willamette Valley. Others put their wagons on rafts to float down the Columbia River Gorge. A lot of folks didn't make it," he said. "Or they lost everything in the rapids."

LaFont and Leslie rode the tug toward The Dalles Dam. A hill on the left was capped with many power lines. "Celilo Converter Station," said LaFont. "That's where they convert electricity from alternating current to direct current. AC is how we use it," he said. "DC is how we send it long distance. That power is going all the way to Los Angeles," he said. "Non-stop."

 In spring and summer, he explained, the Northwest sells power it doesn't need to California. Because of air-conditioning, California uses more power in summer. In winter, California might return power to help heat the Northwest. "Exchanges," he said, "even out peaks and valleys in the way different areas use electricity. They're a good deal for everybody."