BOISE, Idaho (AP) — For years, if not decades, the South Fork of the Boise River has been as reliable as a Swiss watch and as consistent as tax day.
That all changed when wildfires swept through the canyon in August and then a powerful rainstorm in September triggered massive mudslides that poured immeasurable tons of sediment into the river.
The river that typically runs clear as spring water almost year-round was a muddy mess, and the river bed was reconfigured by rocks, logs and mud.
One of the first questions on everyone’s minds would be the fate of the river’s prized fish population. Despite assurance from biologists that slides are natural phenomena and fish are well-equipped to deal with them, anglers remained concerned, but were unable to see for themselves because the Forest Service closed access to the river in late summer. That closure was lifted Nov. 6, and anglers have returned.
HOW’S THE FISHING?
The short answer is the fish appear to have weathered the storm fine so far.
“All in all, I see good fishing ahead for the remainder of fall and winter,” said John Wolter, longtime South Fork angler and owner of Anglers fly shop in Boise.
Wolter and Todd Packer of Boise have, between them, decades of experience on the river. I joined them Nov. 7 for a reunion with the South Fork.
In a day of fishing, we landed lots of rainbows and whitefish. The size of the trout ranged from about 4 inches to one 19-inch, hook-scarred veteran of the South Fork.
“I was pleasantly surprised by the number and size and size differences of the fish we caught, and the health. They don’t look like they’ve missed a meal,” Wolter said.
We fished mostly in the upper river within the first few miles of the dam and found fish well distributed, even in the areas recently disturbed.
“I was also pleasantly surprised by the number of fish in the heavily affected areas, and taken aback by the sheer amount of debris that’s been put in the river,” Wolter said.
We also saw fish rising to baetis mayflies (blue-wing olives) and caught numerous fish on the surface, despite it being a cold, wet, windy day.
Most fish were caught on nymphs, and late fall and winter are traditionally prime times for nymphing while the river is at its lowest flows of the year and easy for wading and accessing prime holding water.
The river is flowing 300 cfs, which should continue until spring.
WHAT DOES IT MEAN?
It’s hard to judge a river “saved” or “recovered” based on one day of fishing, but the mix of fish and the number of them was encouraging. A healthy trout population has a mix of ages, and the South Fork appears to have retained that.
Biologists also surveyed the river since the slides and found many fingerling trout have survived, which are the most vulnerable to mortality from the slides.
“I imagine there are impacts, but they’re not catastrophic,” said Joe Kozfkay, Fish and Game’s southwest region fish manager.
“We were really encouraged to see fry survival and survival of sculpin.”
Sculpin need gaps between larger and smaller rocks to hide from predators, which could fill with sediment after mudslides. Seeing those fish means their habitat hasn’t drastically changed.
Rivers also tend to be more productive years after fires because new nutrients wash into the river, including downed trees that provide good forage for insects.
ON THE RISE
Probably the biggest surprise was to see the number of rising fish that we did on a cold, wet, windy day.
In September, Dr. Chris Walser, professor of biology at the College of Idaho and a stream ecology specialist, said mayfly and midge populations are expected to quickly recover.
Those are the most common insects hatching on the river from late fall to early spring.
Walser expects those insects to recover within months to a year after a fire, and potentially in greater abundance than before the fire.
“We should expect total numbers of stream insects to immediately drop along the burned area, particularly in those areas where mudslides have occurred,” he said in September. “Other studies in different parts of the Western U.S. report that all insect types were immediately impacted by fire.”
Other insects, such as stoneflies, may need two to four years to recover.
Stoneflies typically hatch in late May and June and provide exciting fishing on the South Fork, as well as lots of food for trout.
The speed with which insects recover also depends on whether there are repeated slides, and their severity if they occur.
SEDIMENT AND CLEAR WATER
The river was also running clear, and despite sediment in the river, most riffles still have a cobble bottom.
Unless another mudslides hits the canyon, or there’s one upstream from the dam, the river should remain fairly clear during winter flows.
There are several sections of the river that were partially dammed, causing a backup of slack water, much like a low overhead dam or a weir. This will give anglers new fishing spots to explore and will likely be where there are insect hatches and fish rising to the surface during low flows.
The Forest Service has kept the river corridor closed to camping, and the camping closure will extend “through winter and most likely into early summer,” said Boise National Forest spokesman David Olson.
“The concern is still for the potential of a mudslide or flash flood event,” he said.
Most of the river canyon from Anderson Ranch Dam to Danskin Boat Launch about 10 miles downstream burned, some areas in patches and others completely.
The large stands of cottonwood trees in the river bottom were hit particularly hard.
It’s difficult to tell during autumn which trees are dead and which lost their leaves during fall, but it’s safe to say there are a lot of standing dead trees in the canyon.
Anglers and others should avoid being near burned trees, especially on windy days.
Those trees are also likely to pose hazards to floaters when they fall in the river and drift downstream.
A new rapid formed by a slide between the Tailwaters and Reclamation Village boat launches. A log wedged between large rocks in the channel, and another log parallel to the shore could easily block the river if it swings perpendicular to the current.
But spring will bring higher flows, which could clear some debris and potentially wash more into the canyon, so people should pay close attention to the river because it is constantly changing.
More than 80 volunteers from Trout Unlimited, Boise Valley Fly Fishers, Fly Fishers of Idaho, Women Fly Fishers of Idaho, the Forest Service, veterans and Mountain Home Airmen planted 415 plants and 70 willow cuttings on a recent weekend.
The work will help restore vegetation near the river and stabilize soil on the canyon slopes.
“The incredible response to our call for volunteers shows the love and concern people have for the South Fork. The energy and enthusiasm was unmatched and made this work go very quickly,” said Darryl Kuhrt, of the Ted Trueblood Chapter of Trout Unlimited.