So you’re a salmon heading upstream this fall. It hasn’t rained much for months. The water is low. You reach a culvert that takes the stream under a state highway. The culvert was installed higher than it should have been. In February, water may gush through the pipe. But now, when the water level is low, it doesn’t even reach the pipe. Guess you won’t be spawning this year. Or any year. Sorry about that.

Now — too late for you, but maybe not for the relatives that will try to spawn in later years — the 9th U.S. Circuit Court of Appeals has decided the state must do more toward fixing its hundreds of culverts.

The court affirmed a lower court decision ordering the state to replace its worst salmon-killing culverts that block passage upstream for the fish. A unanimous three-judge panel held that the culverts violate federal treaties signed with Washington tribes.

When the 9th Circuit ruled for the feds and tribes on appeal, it scathingly rejected the state’s arguments and even its math. For one thing, the court found the state’s cost estimates — running to $1.9 billion — were “dramatically overstated.”

This case really goes back to issues raised nearly half a century ago, and its legal underpinnings stretch back more than a century before that.

Some observers think this decision points toward a future court order to breach the four lower Snake River dams, which currently make it harder for salmon to reach high-altitude spawning streams in the Idaho wilderness. Logically, that’s not much of a reach. But legally, it may be. Many legal details are different, not least the fact that the federal government owns and defends the dams, while in the culverts case, the United States, in its role as trustee for the tribes, has joined a group of tribes to sue the state.

The state has petitioned the 9th Circuit to re-hear the case with all judges taking part. The court issued such a sweeping and sharply worded decision that Las Vegas would probably give you pretty good odds against the state winning on appeal. But the state agencies involved could presumably appeal all the way to the Supreme Court —likely for the ultimate judicial slapdown — but for now, the 9th Circuit panel decision is the law.

The new decision may be the most important ruling on treaty fishing rights since 1974.

The treaties date to the 1850s, when Washington’s territorial governor, Isaac Stevens, signed pacts with the tribes so that the United States could gain clear title to most of their land. The treaties said the tribes could always take fish at their “usual and accustomed” places, “in common with” non-native inhabitants.

By the mid-20th century, no one really knew what that language meant, but tribal members fished in the rivers and, increasingly, the state arrested them, sometimes with gratuitous force. In 1970, the United States sued Washington to determine what rights the treaties actually guaranteed. Four years later, U.S. District Judge George Boldt ruled, essentially, that the treaties reserved to the tribes a right to take up to half the fish.

The state resisted, appealing the decision and encouraging people to believe that it would go away. “Except for some desegregation cases,” the 9th Circuit observed in 1978, “the district court has faced the most concerted official and private efforts to frustrate a decree of a federal court witnessed in this century.” The Boldt decision didn’t go away. The U.S. Supreme Court upheld it.

But the case had raised questions that Boldt didn’t answer. He had divvied up the fish but deferred until later the question of whether the treaties guaranteed the tribes an environment in which fish could actually live.

In 1980, U.S. District Judge William Orrick decided that indeed, the right to catch fish meant nothing if there were no fish. So, yes, the treaties guaranteed an environment that could produce salmon. Five years later, the 9th Circuit said not so fast. The environmental right existed, but it could on the basis of “concrete facts which underlie a dispute in a particular case.”

Culverts created and maintained by the state offered the tribes some attractive concrete facts.

Seattle attorney John Sledd, who argued the recent 9th Circuit case for the tribes, explains that culverts clearly have significant impacts — nearly 20 years ago, state agencies estimated that they reduced salmon runs by some 200,000 fish per year. And the remedies are straightforward; replacing pipes under roadways is basically just a matter of spending money.

In 2001, the tribes sued the state over its culverts. Six years later, U.S. District Judge Ricardo Martinez ruled that the culverts did violate the treaties. In 2013, he ordered the state departments of natural resources, parks and recreation, and fish and wildlife to get fish through their worst culverts within three years and ordered the Washington Department of Transportation, which maintains most state culverts, to get fish through the worst of them within 17.

The state appealed. We don’t actually know which state agencies wanted to fight Martinez’ decision and which wanted to comply. Obviously, the fighters won. And now they’ve lost. Again. The 9th Circuit has upheld the district court decision on every point.

Arguably, Martinez’ 2007 decision was the real landmark. Lewis and Clark law professor Michael C. Blumm and Jane G. Steadman have called it “the most important treaty fishing rights decision since the Supreme Court’s affirmation of Judge Boldt some 30 years ago.”

But then, Orrick’s 1980 decision looked like a landmark, too. This time, however, the lower court decision has been resoundingly affirmed. Blumm calls it “a complete and utter victory for the tribes and the federal trustee.”

Judge William Fletcher, who wrote the 9th Circuit opinion, seemed taken aback by the argument that the state could in theory wipe out the salmon without violating the treaties. Fletcher’s written decision quoted from oral argument:

“The Court: Would the State have the right, consistent with the treaty, to dam every salmon stream into Puget Sound?

“Answer: Your honor, we would never and could never do that. …

“The Court: … I’m asking a different question. Would you have the right to do that under the treaty?

“Answer: Your honor, the treaty would not prohibit that.

“The Court: … Let me make sure I understand your answer. You’re saying, consistent with the treaties that Governor Stevens entered into with the Tribes, you could block every salmon stream in the Sound?

“Answer: Your honor, the treaties would not prohibit that.”

The state had argued the same thing back in 1980. It seemed like a loser then — “I was sure we had won the case when the state said ‘we can kill every fish,’” says a lawyer who represented a tribe at the time. “I could see the eyes roll” — but ultimately, it wasn’t. This time was different. The state’s position was just a theoretical extreme, but its effect seemed more than theoretical. Blumm thinks the argument “obviously influenced” Fletcher. Sledd says, “I think that kind of extreme position did not sit well.”

The 9th Circuit’s logic could easily be applied to, say, federal dams, but the facts of this case don’t necessarily translate to other salmon questions. Still, Blumm says that at the very least, the ruling has implications for culverts in other Northwestern states. Beyond that, it’s hard to say.

Even without expanding its scope, the decision is “a great step in the right direction,” says Wild Fish Conservancy’s science and research director, Jamie Glasgow. However, Glasgow says, “While I think we should celebrate, there’s still a whole lot to do.”

He points to culverts owned by counties, private citizens and the U.S. Forest Service. He notes that structures on properties between road crossings also block some streams. And he says that railroad embankments, often built on the flat land near stream mouths, block miles of waterways. Some Forest Service officials are well aware of the problem, but “they have just a fraction of the funding they need.”

Should it take treaty litigation to keep people from blocking salmon streams? No. Washington has had laws against it as long as there’s been a Washington — longer, actually. The current state was once part of the Oregon Territory, and Oregon’s very first territorial legislature passed legislation that forbade blocking salmon streams. From that day to this, though, environmental law that should protect fish has frequently hasn’t been enforced.

“If it was,” Glasgow says, “I’d be out of a job.”

No danger of that. And no danger of the tribes’ environmental rights being settled any time soon. The 9th Circuit decision is “a big deal,” Blumm says. “We’ve been waiting for it for what, 46 years.” And yet, it’s hardly the end of the story.

The meaning of Boldt’s decision and ultimately of the treaties will keep evolving. Slowly.

“I’m afraid.” says Sledd, referring to a Charles Dickens novel that features an intricate and nearly endless civil case, “we may be on our way to putting Bleak House to shame.”

Reprinted with permission from Crosscut.com, a daily, non-profit news site based in Seattle covering public affairs in the Pacific Northwest.