LEWISTON - The big barges and small cruise ships are almost a surreal sight as they sail past dun-colored farm fields and bare hills in the arid landscape of the inland Northwest.

But sail they do, to the western edge of the Rocky Mountains, through a breathtakingly deep valley carved by the Snake River, to Idaho's only seaport.

The Port of Lewiston is the inland most seaport on the West Coast, more than 400 miles from the Pacific Ocean. A series of dams and locks completed on the Snake in 1975 allow ocean-based commerce to be conducted here, and in two nearby ports in Washington state.

But business has dropped sharply at the port, to 1970s levels, just in the past year, prompting longtime critics to suggest that the port - which gets about 20 percent of its $2.29 million annual budget from local property taxes - may not be economically viable in the future.

The chief critics are environmental groups which have been fighting for years to have the four Snake River dams breached because they contend the structures have decimated wild salmon runs.

Port director David Doeringsfeld said the number of ships calling on Portland, Ore. - where cargo from Lewiston is transferred to oceangoing vessels - has been down the past couple of years because of the worldwide recession, and that hurts his ability to ship.

"A lot of our customers have had to truck containers to the ports of Seattle or Tacoma to be able to find carriers to get to their customers overseas," Doeringsfeld said.

At the same time, some of the port's traditional customers in the wood products and grain industries have switched to truck transport permanently.

Currently, the biggest categories of products shipped in containers from the port are paper, dried peas, lentils and grain. And not too much of those.

The port shipped 675,000 tons of wheat in 2007, but had shipped just 388,000 tons by the end of September this year. Perhaps more telling, the port shipped 12,545 containers in 2007, but only 2,325 so far this year.

Business is about to take another dive, as river shipping shuts down on Dec. 1 for three months of maintenance work on the locks.

Sam Mace of Save Our Wild Salmon, a coalition of dozens of environmental groups, said the port provides relatively few jobs, despite the enormous costs to the iconic fish.

After laying off three workers last year, the port has just seven employees, Doeringsfeld said, although more people work for private businesses at the site.

Mace said people are starting to question long-held assumptions that the port makes economic sense.

The government has spent hundreds of millions of dollars in past years in an effort to save salmon. That includes building giant fish ladders to allow the salmon to swim up and through the dams, or using tanker trucks to drive fish around the structures during their migration to the ocean.

The spending was justified on the grounds that the port was a big economic engine, Mace said.

"There is a growing recognition that it's time to do a more honest economic analysis of what the Snake River could provide Lewiston and Clarkston when free-flowing," Mace said. Major benefits would include thriving commercial, recreational and tribal fishing for salmon, which would provide far more jobs and money than the Port of Lewiston, and the nearby ports of Clarkston and Wilma in Washington, Mace said.

Port supporters acknowledged the business outlook is grim in the near term. But the port will survive, said Jerry Klemm of Lewiston, who is head of the Lewiston-Clarkston Chamber of Commerce natural resource committee, and also a port commissioner.

Klemm said there was skepticism locally when the port was proposed in the 1950s.

"Now that we have an economy, locally and regionally, that depends on river navigation for subsistence, it is very important to us," Klemm said. "We'll make it through. It will be lean."

The survival of the four dams is a flashpoint of Northwest politics, pitting environmentally minded Democrats against business-friendly Republicans. President George W. Bush declared the dams were safe under his watch. But the Obama administration has reopened study of the Bush plan to protect salmon, raising the possibility the dams could be breached.

Threats to the dams don't sit well with business groups that have banded together as Northwest River Partners.

"River transport is the 'Prius' of getting goods to market," said Terry Flores, director of the group in Portland. "And it keeps 700,000 trucks off our highways."

Doeringsfeld predicted Lewiston's business would rebound as more ships return to Portland. Using the rivers is two to three times cheaper than shipping a load by truck, he said.

The port is also seeking new business, most famously a project to accept more than 200 pieces of giant oil refinery equipment made in South Korea. The equipment would be shipped to Lewiston and loaded on special transporters for trucking to the massive Kearl Oil Sands project in Alberta, Canada.