The prism of clear river water can distort and magnify the size of a fish, an effect amplified by adrenaline and nostalgia. Still, I remember one fish big enough to shake my whole view of the world.

I was of that tender age when one believes one’s father to be capable of anything – except failure. Dad and I were camping along a headwater tributary of Idaho’s Clearwater River. The trout rose from the shadows of the glassy waters, beyond the reach of my childlike casts. It dashed after my dad’s spinner, but never struck. My mind’s eye sees that fish flashing bright and infuriating, easily eluding us, until the rich evening light faded into darkness.

That fish made my old man mortal in my eyes. It was also my introduction to the bull trout, apex predator of the Columbia River Basin.

Bull trout were formerly called Dolly Varden, which seems like a sissy name for such a muscular fish. They are technically a char, with light yellow dots against a greenish back and fiery orange underbelly. They’re the shape of a salmon and lake-run fish can top 30 pounds. Stories abound of pioneers using pitchforks to collect them from spawning streams to chop into fertilizer, but over the years, the fish population plummeted to habitat degradation, dams, overharvest and competition with exotic species.

Today, I live in the bull trout’s stronghold – the Kootenai and Flathead drainages of western Montana. I’ve watched as the legendary run of bull trout from Flathead Lake crashed. Another run at Swan Lake is drifting into trouble. I’ve also seen the species go from obscurity to headlines when it was listed under the Endangered Species Act. Still, in those Montana waters where the species is holding its own, one may catch – and even keep and eat – bull trout. That’s not just a good thing for anglers; it also reveals the inherent flexibility of the Endangered Species Act.

It surprises many that fishermen are still allowed to pursue bull trout under the act, that notorious “atomic sledgehammer” of a law, as the ESA’s critics have dubbed it. Bull trout were once vilified as a “cannibal fish” that gobbled up more desirable species. Similarly, some politically motivated people vilify the Endangered Species Act as a destructive law, going far beyond objective need or reality. Thanks to that law, which was celebrated May 18 as “National Endangered Species Day,” we as a people recognize that all life deserves respect and that we are all part of the intricate web of life.

Regulated sport fishing rarely contributes to the demise of a fish species, but it has contributed to the rescue of some. Bull trout, like too many native trout, char and salmon species of the Columbia Basin, face a variety of threats, including dams, competitive exotic species and anything that degrades clear, cold spawning streams. All of these have far more damaging and permanent impacts on the survival of endangered fish than does well-regulated sport fishing. And that means that, in turn, fishermen can be a fish’s most powerful political allies, especially when they’re working together with groups such as Trout Unlimited.

The Endangered Species Act does protect the habitat of endangered species, mostly on federal land, and in general, it usually bars the “take” or killing of members of a troubled species. But there are important exceptions. Even where bull trout are listed as a threatened species, they can still be fair game for well-managed sport fishing under section 4d of the Endangered Species Act.

The fact is, a fish species can be faring poorly overall, but still have enough of a surplus in a local population to support a moderate harvest. Between 2004 and 2010, Montana’s Koocanusa Reservoir and Hungry Horse Reservoir of the South Fork of the Flathead River offered about 43,000 days of fishing and produced more than 2,500 healthy, locally produced bull trout meals. Likewise, Lake Billie Chinook, north of Bend, Ore., has a growing reputation as a bull trout fishery.

Within proper limits, sport fishing in such habitats has negligible impact on the population. On the plus side, it introduces thousands of people to the fish and gives them reason to become invested in conservation. With good luck and hard work, fishing opportunities will expand as the species recovers.

My own son likes fishing the kiddie ponds these days, delighted with a 10-inch rainbow trout fresh from the hatchery. Someday I’d like to take him to some remote mountain river and show him a bull trout that’s big enough and smart enough to make a fool of his old man.

Ben Long is a contributor to Writers on the Range, a service of High Country News (hcn.org). He is a conservationist and senior program director for Resource Media in Kalispell, Montana.