Blue is the color of constancy, hence the term
true blue. The unearthly blueness of Crater Lake reflects its pristine character
and gives scientists a focal point for studying human impacts on aquatic
environments over long periods of time. Scientists with the U.S. Geological
Survey (USGS), National Park Service, and Oregon State University have
systematically studied the lake for the last two decades. Long-term monitoring
of this lake is a priority of Crater Lake National Park and will continue far
into the future.
Deepest lake in the United
States and seventh deepest in
Maximum diameter of caldera
at the rim
6 miles (9.7 km)
Average height from Crater
to caldera rim
About 1,000 feet (305 m)
21 square miles (54.4 km2)
1,949 feet (594 m)
64°F (18 °C)
Free-floating microscopic algae
(163 kinds) and animals
salmon and rainbow
trout, both introduced
One of the most dramatic features of Crater
Lake is its blue color; in fact early explorers called the lake “Deep Blue.”
When sunlight penetrates into the lake, the red through the green portions of
the light are preferentially absorbed by water and suspended particles. The blue
light, which penetrates more deeply, is eventually scattered by water molecules
and returns to the lake surface and our eyes. Concentrations of nutrients such
as nitrogen and phosphorus are low in the lake, which explains why growth of
microscopic plants (called algae) is low. The blueness of water is greatest when
densities of particles and algae are low.
Geologists have determined that Mt. Mazama in
southwestern Oregon erupted and collapsed 7,700 years ago, leaving a deepsided
hole called a caldera. The hole filled approximately half way with water over a
period of several hundred years to create Crater Lake. Native Americans tell a
parallel story of lake creation. Llao of the Below World lived in Mt. Mazama.
Skell of the Above World descended to Mt. Shasta, to the south of Mt. Mazama, to
do battle with Llao on behalf of an Indian chief’s daughter. Skell collapsed the
top of Mount Mazama to imprison Llao forever beneath the world. Skell wanted
peace and tranquility to cover up this dark pit, so he filled it with beautiful
Early Scientific Exploration
In the late 1800s, William Gladstone Steel
recognized the importance of Crater Lake for scientific understanding. He funded
scientific surveys of the lake, which encouraged President Roosevelt to sign a
bill in 1902 giving Crater Lake national park status.
In 1886 a USGS crew carried a half-ton boat up
the slopes of the mountain and then lowered it to the lake. Using a pipe and
piano wire, they measured the depth of the lake. Their maximum measured depth
was only 47 feet (14.3 m) more than sonar measurements made in 2000.
In 1896 an adventurous science crew rowed out
across the lake. One member had a white dinner plate in his pack. His objective
was not lunch but rather the first record of lake clarity, which he measured by
lowering the plate into the lake on a rope and recording when it disappeared
from sight. Since then, a black and white disk, known as a Secchi disk, has been
used to measure the lake’s clarity. Clarity in August averages 98 feet (30 m),
but values as high as 142 feet (43 m) have been recorded in the last two
decades. Changes in clarity are related to the amount of algae in the lake and
the transport of sediment into the lake. Crater lake is the clearest measured
natural body of water in the world.
Diving into the lake’s biological mysteries is
the job of federal scientists like Gary Larson and Mark Buktenica. They and
their university partners study a host of lake characteristics. For example,
they teamed up with university professor C. David McIntire to determine that
plant plankton occurs at unusually deep depths in Crater Lake, which is partly a
result of great light penetration in the lake’s clear water. The plant plankton
uses this sunlight to produce oxygen through the process of photosynthesis.
Because of the extreme clarity of the lake, the maximum amount of photosynthesis
occurs between 131 and 262 feet (40-80 m). Plant plankton in the lake is rich in
number of species but the abundance of any single species tends to be sparse.
Furthermore, different forms of plankton, both plant and animal, live at
different depths, down to about 600 feet (200 m).
The animal life includes small and large forms
of invertebrates as well as fish. Eleven kinds of zooplankton inhabit Crater
Lake: nine microscopic rotifers and two crustacean zooplankton. Rainbow trout
and kokanee salmon inhabit Crater Lake, both introduced by people decades ago.
The trout tend to frequent the shoreline, and the kokanee salmon live mostly in
the open water down to a depth of about 450 feet (150 m).
A barometer for Change
Crater lake is a world-class laboratory because
it is pristine except for the consequences of fish introduction. As a national
park it has a high degree of protection from human activities. Long-term
monitoring of Crater Lake is providing a baseline of information about the
natural dynamics of the lake. This baseline serves as a reference when
researching changes in Crater Lake itself and in other lakes around the world.
Research at Crater Lake continues as a collaborative effort of the USGS,
National Park Service, Oregon State University, and others. As research
continues, we learn more about the lake and monitor our success at managing it
so that future generations also can marvel at this deep blue wonder.
Fact sheet written by:
Gary Larson, USGS Forest
and Rangeland Ecosystem Science Center, Mark Buktenica, Crater Lake NP, and Robert Collier, Oregon State University
Fact sheet designed by:
For More Information
Information and Outreach
USGS Forest and Rangeland
Ecosystem Science Center
777 NW 9th St., Suite 400
Corvallis, Oregon 97330
Crater Lake National Park
PO Box 7
Crater Lake, OR 97604