PORTLAND, Ore. — Hundreds of thousands of salmon are making their way from the ocean up the Columbia River this month, a windfall for salmon eaters, and for tribal and recreational fishermen in the Pacific Northwest.

It’s one of the largest runs since dam construction blocked fishes’ river passage. The run is forecast at 1.5 million adult and young adult salmon by year’s end, although fish managers say the final number may turn out to be lower.

“It’s a huge run of fish. It’s been a really good fishing season,” said Rex Zack, a tribal fisherman from the Yakama Nation who has fished the Columbia for 25 years and was hauling in fish near the Bonneville Dam on Friday.

Zack, who runs three boats with the help of his wife, nieces and nephews, said he’s averaging two to three totes of salmon per boat a day — which translates to several thousand pounds of fish. His family keeps some of the salmon to feed themselves and sells the rest.

“It’s really good to see fish coming back,” Zack said.

Millions of salmon once returned to the Columbia. For millennia, the fish were central to Native American culture, sustenance and trade, but the runs were decimated by overfishing, logging, mining, agriculture and hydroelectric dams, which cut off passage to upriver spawning areas in native streams.

Fish hatcheries have been used to help rebuild dwindling fish populations, with mixed results, and millions of dollars have been spent on habitat and dam passage improvements. Thirteen species of salmon and steelhead are now listed as endangered or threatened under the Endangered Species Act in the Columbia River basin.

Some of the fish populations — notably the fall chinook salmon — have increased in recent years. Last year’s record run consisted of nearly 1.2 million adult and young adult chinook.

By comparison, in 1938, a little over 200,000 fall chinook came back to the river. Historically, the runs have seen spikes in numbers every 10 to 15 years.

So far this year, more than 460,000 adult chinook have passed over the Bonneville Dam’s four fish ladders, and the run is a little more than halfway done. About 49,000 jack chinook — the young adult fish — have also made it back over the dam. Bonneville is the first dam salmon cross in their migration upriver.

Monday’s 67,521 chinook were the largest single-day return since the dam was built in 1938. But the daily count of chinook dropped by Friday, leading fish mangers to predict the run may not be as large as originally forecast. On Thursday, the last available daily count, 26,034 fish passed over the dam.

Fish managers attribute the large run to excellent ocean conditions, improved habitat for juveniles heading out into the ocean, and improved fish passage over the dam.

“We’re very excited about the numbers we’re seeing,” said Jason Sweet, fisheries biologist with the Bonneville Power Administration. “It’s an indication that a lot of work we’re doing has been benefiting the fish. It’s thanks to the partnership between federal, tribal, state and nonprofit organizations in the region.”

Sweet concedes that a lot of the returning fish are hatchery-bred, a criticism by some environmentalists who say wild runs are nowhere near being recovered.

That could pose a challenge for long-term success of the runs, because hatchery fish lack the life history diversity and genetic diversity that wild fish have — and hence lack the resiliency to changing environmental conditions, said Bill Bakke, director of the Portland-based Native Fish Society. That results in “boom and bust” runs, he said.

“What we have is periodic large returns every 10 years, followed by lower returns,” Bakke said. “If there’s good habitat and good ocean conditions, they’re successful. Otherwise, they languish.”