In 1996, scientists caused anexperimental flood of the Colorado River by releasing water from Glen CanyonDam above the Grand Canyon. Because an unintentional flood in 1983 had reducedthe river`s introduced population of nonnative trout, biologists were concernedthat the experimental flood would wash many fish, native and nonnative,downstream. To find out, biologists placed nets in the river. The nets captureda few more trout than they would have without the flood but did not showsubstantial flushing of native fish, whose ancestors had, after all, survivedmany larger natural floods. The biologists surmised that the native species(and most of the trout) must have quickly retreated to protected areas alongthe riverbank.