DURANGO, Colo.—Somewhere beneath the turbid, rushing waters of the Animas River are the trout, finning against the current.

After some 3 million gallons of toxic mine water spilled into this big, western river, the economic costs are being tallied by farmers, fly fishing shops, and bankers. Politicians are pointing fingers at each other. It is no accident that federal and Colorado officials have tried to put the best face on disaster. The former actually triggered the incident and the latter have a tourist season to save.

While the Animas disaster avoided immediate and catastrophic results, the ultimate ecological price tag will take longer to figure. The river moves so fast that it swept obvious toxins downstream quickly. Yet the long-term toxicity reached hundreds and, in some cases, thousands of times over what is considered safe for the life beneath the river’s surface. That price will be silently calculated over months and years—by the trout.

Summer in the southern Rocky Mountains means many different things to tourists and locals—but to both, it means trout. These swift creatures can be caught by hook, line, and lowly worm or elite dry fly. The road trip to doing so is half the fun of summer, as Colorado author John Gierach wrote: “Just to be on the road is good in a deep American way but to be on the road going fishing is almost too good for words.”

But by hanging over a boulder or bridge, trout can be observed, too. They are perfect creatures of their habitats, apex predators in a crystalline world of insects, dace, and crayfish. Trout are flawlessly hydrodynamic, with bullet-shaped snouts and skin so smooth that scales seem to vanish. They hover patiently behind rocks, dart into the swift current for food, or push upstream against massive currents.

Far more than a sportfish, the trout is a living filter, a sample, of the river itself.

It not only rakes hyper-oxygenated water over its gills but soaks up the river itself through the permeable membranes of its body. At the Glenwood fish hatchery in New Mexico, a second-generation hatchery worker, Laura Lee Hammer, explained how too much carbon from an old forest fire can kill. An unusual bloom of nitrogen will cause fish to crowd a raceway to avoid contact, she said: “They’re like sheep that way.” The hatchery assiduously maintains pH levels between 6.0 and 9.0 of acidity.

Yet across the West, thousands of old mines hang like chemical swords of Damocles over the clear, rushing world of the trout. The mine above Durango, Colorado—the Gold King—that spilled its contents earlier this month was shuttered in the 1920s. The mine is just one among 500,000 in the United States. The cost of cleaning them up fewer than 200 hardrock mines alone is estimated between $24 and $54 billion.

But no one—no humans anyway—wants to pay those bills directly, or even indirectly. So, some 50,000 mines linger in a federal backlog, namely in the West, and only one in 10 of these has been repaired. Old mine owners have vanished into history and new owners say they have no responsibility for what took place years ago. In Washington, the mining industry has even sought federal indemnity from future lawsuits.

Yet even before this disaster, the Gold King spelled trouble. The creeks connecting it to the Animas were frequently polluted as water interacted with toxic chemicals which, in turn, leached heavy metals from the rock. The Gold King was such trouble it was a candidate for federal Superfund dollars. But a coalition of local interests reportedly didn’t want the stigma that came with federal money; it might frighten off tourists and their money.

After all, the town and the river that ran through it made for a spectacular scene. Big waters teemed with rainbow, cut throat and brown trout just off, say, 32nd Street, a fishery so good that anglers would travel from all over the world. Nearly 100 feet wide in places, the water muscled its way over giant rocks and down into deep holes, so abundant with trout that the state awarded the river its coveted gold medal fishery status.

But trouble appeared last year and it was the trout that told it. Some fish, about 120,000 in recent years, were stocked and some were wild. In 2014, though, state game officials found that the population of fish—particularly young, wild brows, which are perfect monitors of a river’s health—had actually declined. This was the first time in nearly 20 years that the river did not meet the state’s gold-medal standard. And while the precise cause wasn’t clear the eyes of local conservationists turned upward toward the Gold King, by then a troubled wastewater treatment operation poisoning creeks.

Yet nothing was done. So, when a government contractor for the Environmental Protection Agency accidentally breached the Gold King’s water on August 5, the giant orange bloom horrified residents and tourists alike. Santa Fe photographer Tim Harman witnessed the bloom from a nearby roadside, recalling: “I just wanted to cry.”

In contrast, federal officials were quick to declare that the river was rapidly returning to normal as the visible effects swiftly moved downstream. Of course, that is what big rivers do: They push things downstream. The Animas normally flows at over 500 cubic feet per second. What is left behind, however, will not be measured as quickly as that visible, orange plume.

Humans can choose not to drink water with arsenic and lead levels 800 and 3,500 times that considered safe. But the fish had no such choice and were exposed to levels of lead, arsenic, and cadmium 200, 24 and six times, respectively, more than what is considered safe. The pH levels reached about 3.5. (Pure water is about a 7.0.) The EPA cheerily claimed that was about the same as coffee— yet most pH charts actually put the water closer to the  acidity of vinegar.

And that is twice or three times what hatcheries consider safe for trout. Of even greater concern over the longer term are heavy metals. The Farmington Daily Times reported manganese and iron above safe levels. The Albuquerque Journal estimated that as much as 110 acres of river bottom may be covered in toxic sludge as much as an inch thick. Trout not killed outright in a chemical spill can still record the effects in their flesh; browns, in particular will absorb heavy metals over years.

Yet this river is hardly alone. There are over 1,000 chemical spills in the United States each year. In Pennsylvania nearly a decade ago, a spill into Portage Creek was so toxic that desperate trout were seen trying to leap clear of the water; 100 percent of them died in the first few miles of the spill. In Montana, biologists are still trying to understand a 50,000 gallon spill of crude oil into the legendary Yellowstone River.

The county sheriff opened the Animas nine days after the spill yet just in time for the weekend and the tourist season.  Oddly, the crowds of kayakers and fly fishermen did not venture down from the bars and restaurants. A local bank offered emergency loans to fly shops and river guides who had, from their own desperation, put their stock up for sale. Yet by Saturday I still counted not a single fly fisherman on a river where they are normally shoulder to shoulder.

But by their health, behavior, appearance—or absence—the trout will tell what really happened here. The trout always tell.