Researchers at the University of Wisconsin-Madison Center for Limnology created the first map of all the road crossings and dams blocking the tributary rivers that feed the five Great Lakes a few years ago.
These tributaries serve as migratory highways, providing fish like walleye and lake sturgeon access to headwater breeding grounds.
"It painted a pretty horrifying picture of what it's like to be a fish in the Great Lakes Basin," said Peter McIntyre, who led that study.
"Seven out of eight river miles are completely inaccessible to the fish."
The team's new study describes a powerful new model to help decision makers maximise the cost-effectiveness of barrier removal projects that also restore migratory fish habitat.
Recent years have seen growing efforts to chip away at the 7,000 dams and 230,000 road crossings that disrupt the basin's 661 tributaries.
Tom Neeson, lead author of the study, said: "If you're going to spend money on barrier removal projects, isn't it critical to know which projects are going to give you the biggest bang for your buck?"
For example, a $70 million investment to remove 299 dams and 180 road crossings, coordinated across the entire Great Lakes Basin, could double the amount of habitat accessible to migratory fish, the model finds.
That is roughly the amount spent for such projects over the last decade, but until now decision makers have lacked tools for systematically comparing potential projects, the researchers say.
"The bottom line is, you don't have to spend that much money to get a massive return in terms of the amount of habitat accessible for fish," said Mr McIntyre.
As the model matures, its creators say it could ultimately be used to reduce risk of species invasions, plan around aging infrastructure, and account for ongoing climate changes.
The research team recently used the model to launch a free, online tool, called Fishwerks, to help select barrier removal projects that open more fish habitat at lower cost.
"This is one of the pieces I am most excited about," said Matthew Diebel, a co-author on the paper. "A lot of tools don't get used because they can't be accessed by decision makers."
Overall, the study examined the value of efforts coordinated both in time and in space to open more riverine highways for migrating fish.
Marrying high-quality data with high-power computing, the researchers found that for a given amount of money, barrier removal projects coordinated across the entire basin are nine times more cost-effective than projects completed at county or local watershed levels.
For example, the doubling of habitat achieved through a coordinated $70 million investment would cost $690 million if funding was distributed equally across all tributaries.
Coordination at national or even individual lake levels was virtually as efficient as efforts coordinated throughout the Great Lakes.
"It works fine for decisions about Lake Michigan and Lake Superior to be fairly independent of one another," said Mr McIntyre.
"But as soon as you get below that level of coordination, to the county or watershed scale where a lot of decisions are made, the funding gets spread too thinly, and the model shows you're going to underperform drastically."
The study also showed that annual distribution of funds over a decade is 10 times less efficient than a single payout of the same amount.
While coordinating projects can present challenges, it is not unprecedented in this region, where diverse partnerships under the Great Lakes Water Quality Agreement and the Great Lakes Fishery Commission have been very successful, the researchers say.
However, different groups will need to work together for the best outcomes. For example, conservation groups in one watershed may decide that sending their funds to another nearby watershed to remove a critical barrier may actually be the wisest investment, explained McIntyre.
Mr Diebel said: "We have to be willing to say we're not going to work on this issue in my backyard because there is a better-value option elsewhere."
Additionally, Mr Neeson said the model could be used to help combine distinct types of efforts to save money, such as merging fish needs with infrastructure priorities.
"If you can get conservation folks talking to the Department of Transportation folks, there may be opportunities to do fish passage projects during road maintenance projects and piggy-back conservation and construction at lower net cost," he said.
The researchers say the model will continue to improve with more data, which in turn will amplify the power of Fishwerks. The tool currently supports a crowdsourcing feature they call the "Wild West", where authenticated users can contribute their own data, helping to refine the database available to all users.
"The models we run tomorrow will be better because they will be educated by better data," said Michael Ferris, study co-author.
"Can we extend this model to more complex cases? Can we move forward to help with the more pressing issues the scientists don't know how to deal with or need new ideas to address?"
For example, while barriers have kept migratory fish from reaching ideal spawning grounds, many have also kept out invasive species and pathogens.
"This paper is step one," Mr Ferris said. "Our new work is about good fish and bad fish now. We want the good fish to get to the places they need so they can breed, but we also want to limit the bad fish."
