In the documentary “Dammed to Extinction,” showing at 6 p.m. on Tuesday at the Vashon Theatre as part of the Backbone Meaningful Movies series, researchers following the southern resident orcas recall moments from years past when the animals both captivated and astonished them.

But those who care about the whales argue that now, more than ever, is the time to confront what many say are among the biggest threats to their survival: the four Lower Snake River dams, which have upended the migration of spawning chinook salmon for decades.

The 76 southern residents depend on chinook as their primary food source, but with fewer of them to eat annually, they are facing starvation.

The documentary, directed by Michael Peterson, makes the case that the problem with the Snake River dams has been underestimated for some time, beginning with the obstinance of the Army Corps of Engineers, which built the dams during the 1960s and 70s.

Today, the power they generate is marketed by the Bonneville Power Administration, an agency of the U.S. Department of Energy.

Going further, the film argues that the dams are irrelevant today, no longer serving the purpose they once did, and have decimated salmon returns while pushing the orcas toward extinction.

Peterson’s documentary is premiering at a time when the Washington Department of Fish & Wildlife predicts especially low chinook salmon numbers throughout the Columbia and Snake River basins this year compared to previous counts. Meanwhile, the recent birth of a new calf has left many holding their breath — the odds of survival for newborn calves beyond the first few years are only about 50 percent, according to the Center for Whale research.

One trademark of the orcas is the sounds they make to communicate and echolocate their food — each orca pod in the Salish Sea has its own dialect and call. In his office, Bill Moyer, executive director of the Backbone Campaign, said that he has come to believe the whales are capable of sending messages to people, too. One southern resident, he said, has spoken the loudest above the rest.

J35, or Tahlequah as she is otherwise known, embarked on a widely publicized 17-day journey in Puget Sound last year while continually surfacing the body of her dead newborn calf. The act was a vigil of sorts, Moyer said, adding that he believed what resonated most with the public was the sense of the whale’s grief.

“Nothing could have possibly united people around the issue more powerfully than that orca mother,” he said.

According to Moyer, the Backbone Campaign stepped up its calls for the removal of the dams once the appointed work groups belonging to Gov. Jay Inslee’s orca task force began to convene last year.

In November, the task force prepared a finalized list of recommendations aiming to protect the orcas and support their recovery. While no recommendation to remove the dams outright was put forth by the task force — the state cannot move to take them down without the authority of the federal government — the legislature set aside $750,000 in the two-year operating budget to create a forum intended to start discussions over the fate of the dams.

Facilitated by a third party of local, state, tribal and federal stakeholders, the forum will consider ways to benefit salmon while meeting the needs of the communities and industries reliant on them.

The documentary attributes one reason for the creation of the Snake River dams to the Port of Lewiston, Idaho, the state’s only seaport, which is fed by the Snake and Clearwater rivers and accessible to some ocean-going vessels. Conservationists in the film argue that the dams survive in part because of the seaport and the shipments of grain floated back and forth between them by barge, which they say is heavily subsidized by the federal government.

Without the subsidies, they argue, farmers would look for alternative ways to ship their grain, such as by rail.

Amy Morrison, the deputy director of the Backbone Campaign, agrees. She added that compromises funded by the Legislature, namely increased spill over the dams to allow for salmon to pass, are only a short-term Band-Aid, “and it doesn’t help the salmon as much as what needs to happen.”

“I think that it’s some powerful interests in Eastern Washington that want to keep the dams there and refuse to think creatively about how we can all win on this issue,” she said.

For his part, Moyer said the Backbone Campaign has avoided framing the topic of breaching or removing the dams as an “Eastern Washington versus Western Washington” issue because the fish both connect the state and cross the political divide. People in Eastern Washington, he said, care about salmon too, and everyone has a responsibility to safeguard them.

He added that beyond the Snake River, salmon encounter impediments in local waters as well, including around Vashon.

“We have salmon streams here that people have been restoring, Judd Creek and such,” said Moyer. “But … how about the bulkheads and the riff-raff that are causing the temperature of the beach to go up, or not allowing food to be available to the salmon?”

Moyer added that he believes Washingtonians must work together to find a solution that meets all of the competing needs in the Snake River, saying that much of the state benefits from the dams, including islanders.

“We are complicit in the system that creates the need for such dams,” he said. “We are dependent on the farmers of Eastern Washington as well.”

For Peterson, the director of the film, the dams were a part of everyday life growing up on the banks of the Columbia River in working-class Richland. He produced the movie with a close friend, writer Steven Hawley, whose 2011 book “Recovering a Lost River” inspired him to get behind the camera.

“The more I studied the issue, the more I became from a filmmaker to a reluctant activist,” said Peterson in a phone conversation. “I realized how destructive these dams are and how unnecessary they are.”

Peterson was a veteran visual effects compositor in Hollywood for many years, putting digital renderings of spaceships in the skies of movies such as “Independence Day” or “Star Trek: First Contact.” He said he worked behind the scenes on music videos for Kid Rock, Hansen and Linkin Park and helped produce TV commercials for McDonald’s, Cadillac and General Mills cereal.

But it took a toll on him, and doubting the merit of his work, he returned to the Pacific Northwest.

“The bottom line is, I feel a lot better about what I’m doing right now,” he said.

Peterson hopes his audiences will feel inspired to effect change themselves after they see the film, saying that smaller actions such as calling representatives, signing a petition or going to a rally are valid ways to help move progress forward.

But pressure on legislators, he said, is crucial, singling out U.S. Reps. Cathy McMorris Rodgers, Jaime Herrera Beutler and Dan Newhouse for what he said amounted to misrepresenting both the crisis and the value of the dams.

“They are not responding to what’s best for the salmon and whales. They’re responding to the big businesses and what’s best for them,” he said. “They all live right on the river, and they all say they love salmon, but they distort the facts.”

Peterson said that in spite of political influence weighing in favor of the dams, it is up to voters to decide what they want for the river and who they want to lead its future.

Joseph Bogaard, executive director of Save Our Wild Salmon, said he was interested in helping to bring Peterson’s film to Vashon because of the interest and concern many islanders share about the plight of orcas and the fish they depend on.

But scientists who first identified the relationship between the southern residents and chinook salmon, he said, have been ringing alarm bells for years. He believes it has taken too long for policymakers and members of the public alike to come to their defense.

“There is an urgency here, and we don’t have a lot of time to spare if we want to reverse this decline of orca and salmon [to protect them] from extinction,” he said. “These issues are linked, and they’re moving in the wrong direction, and there’s no time to waste.”

Admission to the theater is free. A question and answer session with Michael Peterson will follow the screening.

This version of the article clarifies who manages the lower Snake River dams.