"It will recover very, very quickly," Rogers assured. With their food sources suddenly plentiful from being stirred up by the experiment, the first 24 hours afterward, he added, the trout may be stuffed and not quite so hungry.

The experiment's timing suits Martha Hahn, chief of science and resource management for Grand Canyon National Park. One key, she said, is to do it before the dense, non-native tamarisk trees and shrubs produce seeds that can be swept downstream, creating what can become a choke-hold on riparian habitat.

Another important element of this experiment, Hahn said, is how to operate the dam after the initial huge rush of water. It's important, she said, not to cut the flow too much, too quickly, risking that the water will drop too fast and then essentially undercut existing shoreline, causing it to collapse.

Hahn was quick to point out Tuesday a small area of sharply sloping shore that has been important to a woman in a nearby boat joining in on the same river trip.

Janet Balsom is the deputy chief of science and resource management for the Grand Canyon National Park. There's a section of shore where she has overseen excavation of an archaeological site that will probably get washed away. Her approach to archeology along the Colorado is preservation first, then, if necessary, excavation.

The problem, however, is that some sites are becoming exposed due to a lack of sediment, or sand, deposited along the banks of the river as a result of the dam's presence. Throughout history most sites have remained hidden because sand and dirt from beaches and shore get moved, usually by wind, around or over sites, in effect protecting them against humans and the elements. There was balance before the dam.

For Balsom, it's been interesting to see the sites in greater detail, but she'd prefer they remain protected and tucked away. As recently as the 1960s, the landscape along the Colorado was such that many sites were not even visible or known. Now, greater exposure means, in some cases, losing sites before they can be excavated or preserved.

"You can't create archaeology," Balsom said about recouping losses that have come over the past 20 years. Currently there are nine sites being actively excavated, also in danger of being lost along the river.

She and others will be watching closely in the months and years ahead how and where sediment deposits settled and how those settlements will interact with irreplaceable archaeological sites. Part of the excitement with this experiment is that there appears to be about three times the amount of sediment waiting to be moved compared to the release in 2004.