Water diverted to stir sediments and save chub.
Gushing through the bypass gates of the Glen Canyon Dam in northern Arizona, the turbid, ruddy waters that once gave the Colorado River its name poured into the Grand Canyon last week at more than twice the usual rate.
The flush was intended to mimic floods that carried large quantities of sediment into the canyon before the dam's construction 45 years ago, which cut the mud flow to 6% of its natural level.
The floods built sandbars and maintained the river's copper colour, enabling the vulnerable native fish, called humpback chub, to hide from predators.
Although the river level temporarily rose by up to 5 metres in the canyon, it is unclear whether the torrent successfully dirtied the water, as the models had predicted.
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Petherick, A. Snapshot: Flooding the canyon. Nature 452, 138 (2008). https://doi.org/10.1038/452138b