June 28, 2026
Selective Passage: Restoring Natural Balance
In Part I and Part II, we explored what it means to take a more natural approach to fish passage—one that aligns with how fish actually migrate, reduces stress, and restores the experience of movement.
But there is a deeper issue we have not yet fully confronted: What happens when we pass all fish —all the time? Because in nature, that doesn’t happen. When we replicate that condition at dams—24 hours a day, 365 days a year—we are not restoring the river, we are fundamentally changing it.
The Hidden Assumption in Fish Passage
For decades, the goal of fish passage has been simple: Move fish upstream. While that goal made sense when infrastructure first blocked rivers, we’ve carried it forward without questioning one critical assumption: That all fish should pass, indefinitely, without distinction. But natural river systems have never functioned that way. They are selective—by season, by flow, by temperature, by behavior, and by species. Barriers exist. Filters exist. Constraints exist. Nature is not indiscriminate.
When “More Passage” Becomes Less Natural
The consequences of non-selective passage are not theoretical. They are visible—and growing. One of the clearest examples exists on the Snake River. Each year, large numbers of American shad—an introduced, non-native species—move upstream in overwhelming volume.
They do not just pass, they accumulate and congest fish ladders. They fundamentally change the system. When that happens, the impacts cascade:
This is not a natural condition. It is a system we have created—unintentionally—by allowing continuous, unmanaged passage.
A River That Never Resets
In a natural river system, fish movement is episodic. Runs occur. Windows open and close. Predator-prey dynamics fluctuate. Systems rebalance. But at modern dams with non-selective passage:
There is no reset. There is no filtering. There is no seasonal constraint. Instead, we have created a perpetual conveyor of biomass, altering energy flows in ways that ripple through the ecosystem and critically, we have done this in the name of restoration.
Selective Passage: A More Natural Standard
If we are serious about restoring ecosystems—not just moving fish—then we need to reframe the objective.
Not: “How do we pass more fish?”
But: “How do we pass the right fish, at the right time, in the right way?”
This is what selective passage makes possible. Selective passage is not exclusionary—it is restorative. It allows us to prioritize native species and ESA-listed runs. It limits the upstream advancement of invasive or non-native species. It restore natural timing and structure of migration and reduces predator aggregation driven by artificial abundance. Rebalance ecosystem energy flows. In other words, it allows us to reintroduce filters that rivers once naturally provided.
Technology as Stewardship
Historically, selective passage was difficult and has never scaled well. It required:
Which introduced stress and delays. But today, that constraint is no longer absolute.
With real-time identification and routing systems, selective passage can occur:
Fish can still choose to enter a system. But what happens next can be aligned with restoration goals rather than left entirely unmanaged.
This represents a shift from passage as access, to passage as stewardship.
The Cost of Ignoring Selectivity
We should also be candid about the alternatives. Continuing non-selective passage:
Perhaps most importantly, it delays meaningful ecosystem recovery—while giving the appearance of progress. From a practical standpoint, it is also inefficient. Managing the downstream consequences of unmanaged passage—predator control programs, habitat mitigation, hatchery supplementation—comes at significant and ongoing cost. Selective passage addresses the problem at its source.
A Faster Path to Restoration
There is a tendency to view ecosystem restoration as a long, incremental process, and in many cases, it is. But selective passage offers something different: A direct intervention at a control point. Dams already concentrate fish movement. They are, by definition, decision points.
Using them intentionally—rather than passively—may be the fastest and most cost-effective way to:
A Better Question
As with the previous parts in this series, the most important shift is not technological. It is conceptual. We need to ask a better question.
Not: “Do we have fish passage?”
But: “Do we have the right passage for the ecosystem we are trying to restore?” Because passing everything, all the time, is not neutral. It is an intervention, and in many cases, it is the wrong one.
Closing Thought
If a more natural way forward means respecting how fish migrate then it must also mean respecting which fish should move—and when. Selective passage is not a refinement, it is a correction, one that aligns with ecology, restoration science, and the values of those who have stewarded these systems long before dams existed. So passage is not just about moving fish, but about restoring natures balance.
Vincent Bryan III
CEO & Founder, Whooshh Innovations Inc.
