Hotter than July STANDING on the banks of the Yellowstone river in southern Montana on the last afternoon in June, Dan Vermillion gazes at the clear, sun-dappled waters, checks the river temperature on his smartphone, and pronounces the conditions “great fishing”. Alas, this does not cheer Mr Vermillion, who grew up fishing these waters for trout and now works as a high-end outfitter, guiding the wealthy and powerful to the world’s best fly-fishing spots, from Montana to Alaska and even Mongolia. For these fine fishing conditions—with the water running clear after months of turbid flows from spring snowmelt, and the temperature at 65°F (18.3°C)—have arrived too early, by some weeks. The water should be ten degrees cooler, frowns Mr Vermillion, and data retrieved by his smartphone from a nearby measuring station shows flows at less than half their historical median level.
All rivers vary from year to year. What worries federal wildlife officials, state biologists and a growing number of devoted anglers across the mountain West, is that, for the past 15 years, some of America’s finest fishing rivers keep breaking records for early snowmelts, too-warm water and low flows. Mr Vermillion is also chairman of the Montana Fish and Wildlife Commission, a government body. To his dismay he has just approved some of the earliest fishing closures ever recorded, closing legendary trout waters on such rivers as the Gallatin, Beaverhead and Jefferson every afternoon with effect from July 1st, after water temperatures hit 73°F (22.8°C) on three consecutive days. Afternoon closures are a compromise, aimed at giving trout a respite in the warmest hours of the day. Trout are cold-water fish, which struggle to digest food above such temperatures, and start to die once water nears 80°F (26.7°C). Warmer water carries less oxygen, too, so that trout caught and released may never recover once back in the river.

Such worries used to be rare. In the six years from 1995 to 2000 water temperatures on the Jefferson river, in south-western Montana, exceeded 23°C on only 23 days, and in some years never went that high. In 2015 alone, the water crossed that danger-mark on 21 days and exceeded 26°C in early July, leading to significant fish deaths. After studying data going back decades, the long-term trends are “exceptionally clear”, says Mr Vermillion. Other signs of stress may be seen. The coldest, highest rivers of south-western Montana are home to the Yellowstone cut-throat trout, named after an orange under-jaw marking like a slash. Smaller than non-native rainbow and brown trout, which were introduced to Montana in the 19th century, the cut-throat is especially sensitive to warming water. Rainbow and brown trout are pushing up into cut-throat fisheries, even into the protected rivers of Yellowstone National Park, where anglers must watch for grizzly bears and snorting, shaggy-headed bison, but increasingly catch hybrid trout, rather than pure-bred cut-throats. Worse, smallmouth bass, a warm-water species, are each year creeping farther and farther up Montana’s rivers. Bass have even been caught near Mr Vermillion’s office in the handsome town of Livingston. Something, in short, is going on. Where consensus breaks down is when locals, scientists, politicians and even fishing clients debate whether what is going on has links to man-made climate change. All too often discussions follow partisan lines, says Mr Vermillion. He is a Democrat in a conservative state: his office wall has a photograph of him fishing with President Barack Obama in Montana (“Dan! You got me hooked,” reads the presidential inscription). His wife’s family, who are conservative farmers, acknowledge that the weather is changing. “Where it gets tricky for them is to admit that it is man-made.” Montana’s three-man congressional delegation splits on party lines: Representative Ryan Zinke and Senator Steve Daines, who are Republicans, call the science of climate change far from proven, and both have opposed carbon-emissions curbs that might hurt their state’s coal and oil industries. Senator Jon Tester and the governor, Steve Bullock, both conservative Democrats, call climate change a threat and back the development of renewable energy in Montana (a windy place), while urging caution over federal policies that would impose rapid change on the coal sector.

Spending by tourists is increasingly valuable, with the state Office of Tourism claiming that 53,000 jobs are supported by visitors. Mining employs fewer than 7,000 people in a state of 1m inhabitants. But coal and oil jobs pay better than tourism work, and energy companies pay a lot of taxes. Still, fish are changing the public discussion about climate change and whether it might be hurting Montana, says Mr Vermillion, who as a wildlife commissioner meets frequently with hunters, ranchers and other groups. Telling people where smallmouth bass have been found is his most effective piece of evidence for convincing audiences that the weather is changing, he notes, trumping dry statistics about rising temperatures, shrinking snow packs and more frequent wildfires. “What bass say about our rivers is spooky."