At this time, nevertheless, 4 of these fish—the humpback chub, the Colorado pikeminnow, the razorback sucker, and the bonytail—are federally listed as threatened or endangered. Lake Powell commandeered the Colorado’s payloads of silt and stymied pure floods, erasing channels and backwaters the place chubs and suckers as soon as spawned and reared. And smallmouth bass and different invasive species devastated native fish in tributaries just like the Yampa River. (“Smallmouth” is a misnomer: Bass have maws so cavernous they will gulp down prey greater than half their very own measurement.) Bass arrived in Lake Powell in 1982, courtesy of a hatchery supervisor who, on a lark, dumped 500 spare smallmouth into the reservoir. The bass, he crowed a long time later, “carried out magnificently,” including, “Anglers have caught thousands and thousands of smallmouth bass over the previous 30 years.”
By way of all of it, the Grand Canyon remained a bass-less sanctuary—thanks, paradoxically, to Glen Canyon Dam. Though smallmouth teemed in Lake Powell, they stayed within the reservoir’s heat, sunlit higher strata, nicely above Glen Canyon Dam’s penstocks, the huge tubes that convey water by its hydropower generators and thence downriver. Bass by no means reached the Grand Canyon as a result of they by no means swam deep sufficient to go by the dam.
As Lake Powell withered, nevertheless, so did the Grand Canyon’s defenses. By the spring of 2022, 20 years of local weather change-fueled drought had lowered the lake’s floor by greater than 150 toes, drawing its tepid, bass-filled high layer ever nearer to the penstocks. On the identical time, the hotter water flowing by the dam and downstream made the Grand Canyon extra hospitable to bass. “The temperature was ideally suited for them,” stated Charles Yackulic, a analysis statistician on the US Geological Survey.
Final summer season, after bass swam by Glen Canyon Dam’s penstocks, slipped previous its whirling generators, and apparently reproduced, managers hastened to manage the incipient invasion, netting off the slough the place Arnold found the juveniles as if it had been against the law scene. The Park Service additionally doused the backwater with a fish-killing poison. When biologists electroshocked the river that fall and the next spring, although, they discovered tons of extra juveniles. The slough wasn’t an remoted beachhead; it was merely a battleground in a broader invasion.
If there’s a saving grace, it’s that the bass stay concentrated above the chilly, clear stretch of river often called Lees Ferry. Humpback chub, in contrast, have their stronghold deep within the Grand Canyon, some 75 miles downriver from the dam, the place bass haven’t proven up—a minimum of not but. “The concern is that you just bought them in Lees Ferry they usually’re reproducing,” Yackulic stated. “After which all of the sudden, you’ve simply bought all these infants dispersing downstream.”