In Western Washington, engineers and conservationists are facing a puzzle that billions of dollars haven't yet solved: removing a dam or culvert that blocks fish from reaching their spawning grounds sounds like a straightforward win, until the fish hit another barrier just downstream and never complete their journey.
This collision between ambition and planning is what drove University of Washington researcher Sunny Jardine to ask a deceptively simple question: Are we spending our fish passage restoration dollars in the smartest way possible?
Fish that split their lives between fresh and salt water—salmon and steelhead among them—depend on unbroken river corridors to survive. Dams and road culverts fracture these networks, triggering cascading threats to fish populations and broader biodiversity. In recent years, states and the federal government have responded by allocating billions toward reconnecting fragmented rivers. Washington state alone is in the midst of a court-ordered multibillion-dollar effort to remove barriers blocking salmon and steelhead from swimming upstream to spawn.
But here's the catch: most of these projects rely on a planning approach called "score and rank," which evaluates barriers one at a time, assigns each a score based on potential gains like habitat expansion, and funds the highest-ranking candidates first. The method sounds logical. In practice, it often isn't.
When researchers in Jardine's lab examined fish passage projects across Western Washington, they discovered something troubling. High-scoring projects frequently created what they call "stranded investments"—situations where removing a barrier yields no real benefit because other obstacles immediately downstream or upstream still block the fish. You've spent millions reconnecting habitat the fish can't actually reach.
"Ideally, barriers that are most downstream will score higher, because they need to come out before the fish can benefit from upstream restoration," Jardine explained. "But approaches to scoring vary, so this isn't always the outcome."
The study, published in PLOS One, presents an alternative: a mathematical optimization program that evaluates barriers as an interconnected system rather than individual candidates. Instead of working barrier by barrier, optimization synthesizes multiple inputs—habitat quality, connectivity, budget constraints—and identifies which removals will yield the greatest collective benefit.
Testing this approach against the current score-and-rank standard in Western Washington revealed nuance. Score and rank performs reasonably well when the sole goal is opening up as much habitat as possible. But introduce other variables—habitat quality, fish population diversity—and its performance falters. Optimization excels at balancing competing priorities, though it requires data infrastructure and mathematical expertise that not every community possesses.
Washington state has already begun hedging its bets, combining score and rank with optimization in a hybrid approach. Yet most fish passage projects elsewhere continue relying solely on score and rank.
The good news: Jardine's research suggests that even modest tweaks to existing scoring systems can rival optimization's results. "Major change is hard, but minor changes may be enough," she said. Given that the total cost of restoring every barrier vastly exceeds available budgets, making smarter choices about which barriers to remove first isn't just about efficiency—it's about ensuring that every dollar spent genuinely returns fish to their ancestral spawning grounds. For rivers already stretched thin by fragmentation, that precision matters.