The New Childrens Encyclopedia

PRECIOUS WATER

49

Underground water Some

of the water that falls as rain

seeps into the soil and into

the rocks below to become

groundwater. Some rocks

soak up water and form a

saturated layer called the

water table. But water can

also leak through cracks in

rocks and form pools in

underground caves.

O

There are approximately

75,000 dams in the United

States alone.

O

Las Vegas gets

85 percent of its water

from Lake Mead—the

vast reservoir behind

the Hoover Dam.

O

At 1,000 feet (300 meters) tall,

Nurek Dam in Tajikistan is the

world’s tallest dam.

Solid water Some water falls from clouds as

snow. In the polar regions, and high in the

mountains, the snow builds up in layers that

push down to form an icy mass called a glacier.

The glacier flows to the sea and breaks up into

icebergs, which gradually melt, and the water

cycle starts all over again.

WATER

EARTH

SAVE FRESH WATER

O

Running faucets uses up a lot

of water, so turn them off when

you have finished.

O

Only flush the toilet when

you have to.

O

Take a shower instead of

a bath because it uses up

much less water.

O

Keep waste water from

sinks and bathtubs and use it to

water plants in the garden.

The world’s longest rivers

(by continent) are:

O Nile: Africa’s longest river,

at 4,135 miles (6,650 km).

O Amazon: At 4,000 miles

(6,400 km), the longest river

in South America.

O Yangtze: Asia’s longest river,

at 3,915 miles (6,300 km).

O Mississippi: At 3,902 miles

(6,275 km), the longest river

in North America.

O Volga: Europe’s longest river,

at 2,294 miles (3,692 km).

O Murray–Darling: At

1,701 miles (2,739 km), the

longest river in Australia.

WORLD’S LONGEST RIVERS

 WATER SUPPLY Lucky Peak Dam

traps water from the Boise River in Idaho.

 The Nile River was the lifeblood

of the ancient Egyptians, providing

the water to grow their crops.

BLIND CAVEFISH
These fish live in deep
caves and rely on touch,
rather than sight, to sense
their surroundings.