Jim Hutchins stands atop two old, exposed sewer line spanning Bear Creek beneath the Jackson Street Bridge, staring at the frothy brown water at the base of this three-foot drop for the next explosion to occur.

On cue, a wild fall chinook salmon the size of a man's leg bursts out of the froth and hurtles itself onto the concrete-covered pipes, only to fall just short and tumble back into the pool.

"Almost got it that time," says Hutchins, a naturalist who monitors Bear Creek chinook runs each fall. "That's 10 fish in 15 minutes. That's about as good as it gets."

Bear Creek's fall chinook run that migrate into Medford each fall in relative anonymity are being outed in grand style thanks to an artificial waterfall that is creating plenty of air time for chinook in Southern Oregon's signature urban creek.

Fish that normally dark through the creek's silty waters instead are forced to dart, jump or power-swim over this new impediment exposed when last winter's heavy flows scoured out several feet of the dirt, rocks and gravel from the creekbed below Jackson Street, one of downtown Medford's busiest thoroughfares.

But so far, most pedestrians along the Bear Creek Greenway are oblivious to this rare snapshot in the collage that is chinook's life cycle in a urban stream that stacks the environmental deck against its underwater downtown denizens.

"This is really great, but I've actually only seen a few people looking," says Hutchins, 81, who has charted salmon migration and counted salmon nests, called redds, in Bear Creek the past 24 falls.

"Just open your eyes," he says.

And open them now.

The City of Medford, which owns the two abandoned sewer lines, and the Oregon Department of Fish and Wildlife are working together to drain and cap the pipes before removing them altogether so salmon can swim unimpeded upstream and downstream past the Jackson Street bridge.

The two agencies today plan to bring in a contractor for some pre-estimates, but city contracting policies and oncoming rains likely mean the pipes remain until next spring.

"We need to get this done by next summer at the latest," says Dan VanDyke, the ODFW's Rogue District fish biologist. "I'm not sure removal will be feasible for this fall. The stars aren't aligning right for that."

That keeps the chinook stars of this show throughout October, with the peak migration through downtown Medford is about a week away, Hutchins records show.

Glimpsing peeks of spawning chinook has been a popular participatory sport from Medford to Ashland each fall, with the curious armed with polarized sunglasses perching themselves at places like the wooden bridge at Hawthorne Park to see female chinook dig egg nests, called redds, and males battling over spawning rights.

But what these salmon do to get there often goes unnoticed.

Born in spring in the creek's gravels, young chinook often struggle during their six-month stay in Bear Creek's water often too warm, too silty and too short of dissolved oxygen for their liking.

Those that survive migrate into the Rogue River, then down to the ocean for one to four years before retracing their steps back to Medford as salmon anywhere from 6 to 40-plus pounds to continue the cycle before dying.

The stretch directly under the Jackson Street bridge has joined the dismantled Rogue River Valley Irrigation District seasonal dam and fish ladder along Hawthorne Park as the two best places to get a don't-blink glimpse of migrating chinook.

Under the bridge, water flowed over a rock-and-concrete structure built decades ago by Pacific Northwest Bell, dropping a few feet into a deep pool that gave chinook plenty of room to garner a good head of steam to clear. When they did, the chinook finned through a shallow glide then immediately over the very top of the old sewer lines with little fanfare.

But last winter, sustained high water scoured out the area between the pipes and the downstream concrete wall, exposing the pipes and digging under what is now a concrete lip. The creek now flows over the exposed pipes, through a shallow pool and then underground for about 15 feet before popping out downstream of the bridge.

Discovered last week, the circumstances alarmed state fish biologists concerned that the subterranean nature of the creek and the high over-the-pipes jump would pose a threat to migrating salmon.

Oregon Department of Fish and Wildlife biologists began considering contingency plans, such as possibly notching the pipe for passage and perhaps even netting and portaging chinook past Jackson Street bridge should salmon key up in the downstream pool.

However, at least some of the chinook have proven capable of swimming under that concrete lip and higher water flows thanks to the end of the irrigation have made the pipe passable to most chinook.

Throughout the day, chinook can be seen jumping or power-swimming over the pipes.

The larger and more powerful chinook often make it after a few attempts, their black-blotched bodies creating v-like waves as they disappear into the pool above.

The younger, smaller salmon often struggle in this latest, but not last, challenge Bear Creek creates for its wild salmon.

"The big, healthy ones can clear it but the weak ones can't," Hutchins says. "Those will still drop down and spawn someplace.

"If they can't adapt, we wouldn't have any fish," Hutchins says.

— Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@mailtfribune.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.