The damaged tubes sit below much larger ones known as penstocks that normally carry the reservoir’s water.

At Lake Mead, the water courses through Hoover Dam’s intakes and rushes through 30-foot-wide pipes called penstocks.

If the reservoir falls much lower, he said, dam managers would need to stop using the main intakes, called penstocks, and could release water only through lower bypass tubes, which have reduced capacity.

Visitors can peer over a glass protector to observe the inner forebay, which, through underwater arches, filtered the incoming water into the plant before it churned through the penstocks.

Other options include penning off areas downstream from the dam where chub congregate or installing structures such as “bubble curtains” to keep nonnatives in Lake Powell away from the penstocks.