Water-Resources Investigations Report 1999–4189 

April 2007

Great Salt Lake, Utah

Introduction

Great Salt Lake, the shrunken remnant of 

prehistoric Lake Bonneville, has no outlet. Dissolved salts accumulate in the lake by evaporation. Salinity south of the causeway has ranged 

from 6 percent to 27 percent over a period of 22 

years (2 to 7 times saltier than the ocean). The 

high salinity supports a mineral industry that 

extracts about 2 million tons of salt from the 

lake each year. The aquatic ecosystem consists 

of more than 30 species of organisms. Harvest 

of its best-known species, the brine shrimp, 

annually supplies millions of pounds of food for 

the aquaculture industry worldwide. The lake 

is used extensively by millions of migratory 

and nesting birds and is a place of solitude for 

people. All this occurs in 

a lake that is located at 

the bottom of a 35,000-

square-mile drainage 

basin that has a human 

population of more than 

1.5 million.

Frequently Asked Questions 

and Answers about Great 

Salt Lake

• How large is the lake?

At the average water-surface altitude of 

4,200 feet, the lake is 75 miles long by 28 miles 

wide and covers about 1,700 square miles. At 

this altitude, the maximum depth is about 33 

feet. At its lowest altitude in 1963 (4,191 feet), 

it was less than one-half the size it reached at its 

historic high peak during 1986–87 (4,211 feet).

• How was the lake formed?

The lake is a remnant of Lake Bonneville, a 

large Pleistocene-age lake that covered about 

20,000 square miles (slightly smaller than West 

Virginia at 24,000 square miles) and was a 

maximum of 325 miles long by 135 miles wide, 

with a maximum depth of 1,000 feet. Lake 

Bonneville existed from about 30,000 years ago 

to 16,000 years ago. Four ancient shorelines 

of Lake Bonneville are visible on the Wasatch 

Mountains to the east.

Altitude

(feet)

Lake-level name Years

before present

4,500 Stansbury 23,000–20,000

5,090 Bonneville 16,000–14,500

4,740 Provo 14,500–13,500

4,250 Gilbert 11,000–10,000

(Curry and others, 1984) 

• When did the lake first appear?

Although as early as 30,000 years ago there 

were alternating periods of saline lakes and playas (salt flats) in the basin, Great Salt Lake is 

believed to have first formed about 11,000 years 

ago when the lake rose from a smaller saline 

body to about 4,250 to 4,275 feet at the Gilbert 

Level. At this time it was about three times as 

large as present Great Salt Lake and was salty. 

The lake was less salty during the Stansbury 

Level of Lake Bonneville.

• Why is the lake salty? 

Because the lake does not have an outlet, 

water flows into the lake and then evaporates, 

leaving dissolved minerals behind as residue. 

On average, 2.9 million acre-feet of water 

enters the lake each year from the Bear, Weber, 

and Jordan Rivers. The inflow carries about 

2.2 million tons of salt. About 4.3 billion tons 

of salt are in the lake, and commercial removal 

of the salt ranges from 1.6 to 2.5 million tons 

annually. 

• What animals live in the lake?

Of the various animals, the most visible and 

famous is the brine shrimp (Artemia franciscana). Two species of brine flies (genus Ephydra) also are very numerous but do not bite. 

Numbers of these flies may reach 370 million 

per mile of shoreline during summer.

Two to five million shorebirds and hundreds 

of thousands of waterfowl use the lake seasonally. Wilson’s Phalarope and Eared Grebes often 

are present in summer.

• How did brine shrimp get into the lake and 

when did they first appear?

The shrimp likely arrived as cysts (eggs) on 

the feet of migratory birds. Brine shrimp cysts 

and fecal pellets in a deep sediment core have 

been dated to be 15,000 years old.

• How do brine shrimp live in the extremely 

salty (hypersaline) environment of the lake?

The body cuticle prevents water loss and salt 

entry. The shrimp drink large amounts of salt 

water and the gut takes up the water (and some 

salt). The branchia, or gills, then excrete the salt 

back into the water.

• Have there ever been marine organisms or fish 

in the lake?

In 1899, the U.S. Fisheries Service considered implanting oysters into the mouths of the 

larger rivers that enter the lake but decided that 

oysters could not be raised commercially.

In 1986, killifish entered from Timpie 

Springs on the south end when the lake was at a 

salinity of about 5.5 percent.

• Why is the north part of the lake purplishpink?

A railroad causeway separates the lake into 

a north and south part. Most freshwater enters 

the south part, and water in the north part 

evaporates faster than it enters. The north part is 

always much saltier than the south part. Several 

species of purple salt-tolerant bacteria and an 

alga with a red pigment live in the north part 

and cause the purplish-pink coloration, especially when the salinity is greater than about 25 

percent.

• Are there any other large saline lakes?

Excluding Lake Eyre in Australia (3,100 

square miles when flooded, but usually dry):

Water body Salinity

(parts per

thousand)

Area

(square 

miles)

Caspian Sea (Russia, Iran) 11 170,000

Aral Sea (Russia) 10 25,000

Lake Balkhash (Russia) 2.8 7,115

Great Salt Lake (Utah) *140 1,700

Salton Sea (California) 44 380

Dead Sea (Israel) 220 390

 * Measurement for Gilbert Bay, 1995.

Adult actual size

History

Thirty thousand years ago, during the last ice 

age, Lake Bonneville expanded from a small 

saline lake to a freshwater lake that covered 

about 20,000 square miles and was about 1,000 

feet deep. About 16,000 years ago, the lake 

cut a massive outlet at its northern end and 

discharged a flood that reached the Snake River. 

A dry period nearly eliminated any remnant of 

the lake about 500 years later, but increasing 

Brine shrimp (Artemia franciscana) adults and cysts.
precipitation raised the water surface to about 

50 feet above the present lake level, creating 

Great Salt Lake.

The Dominguez and Escalante expedition 

reached Utah Valley, 50 miles south of Great 

Salt Lake, in 1776. The indigenous Timpangotzis Indians told them of a very salty lake 

in the valley to the north. The explorers were 

anxious to return to Monterey and did not 

investigate this saline lake. In 1824, the French 

trapper Etienne Provost may have been among 

the first of the European trappers to see the 

lake, but other European trappers and explorers also vie for the honors: Jim Bridger, Peter 

Skene Ogden, and John H. Weber. An early 

scout and explorer, John C. Fremont, is credited with making the first scientific measurement of lake altitude in 1843 (4,200 feet).

The Stansbury expedition entered Salt Lake 

Valley to make maps and describe the area in 

1849 under the direction of the U.S. Government. The expedition succeeded in mapping 

the entire shoreline of the lake by 1850. All of 

the larger islands in the lake except Fremont 

Island were named for members of this exploration party: Stansbury Island (Howard Stansbury), Carrington Island (Albert Carrington), 

Gunnison Island (J.W. Gunnison). 

Clarence King, a geologist with the U.S. 

Government survey of the Fortieth Parallel, 

surveyed the lake from 1869 to 1870. Additional geologic and geographic surveys in the 

vicinity of Great Salt Lake were completed in 

the next few years by F.V. Hayden, George M. 

Wheeler, and Grove C. Gilbert as part of the 

great exploration of the 

West done by the U.S. 

Army Corps of Topographical Engineers 

and the U.S. Department of the Interior.

Hydrology and Salinity

Great Salt Lake is divided by a rock-fill railroad causeway constructed in 1959 to replace 

the wooden trestle built in 1903. During the 

high water years of 1983–87, additional fill 

was added to raise the structure and a 300-foot 

breach was added. Most of the surface inflow 

from the Bear, Weber, and Jordan Rivers enters 

the lake south of the causeway, and only a 

small amount of water flows north through 

openings in the causeway. Water north of the 

causeway (Gunnison Bay) often has a salinSurface-dwelling Birds insects

(Trichocorixa

verticalis)

Commercial

harvest

Decomposition and

nutrient release (bacterial)

Fecal

pellets

Adult Birds brine flies

Shrimp

cysts

?

Nutrients

from the

watershed

Brine shrimp

(Artemia franciscana)

Phytoplankton

(Dunaliella viridis

Pennate and

Centric diatoms)

Brine flies

(Ephydra Larvae)

Bottom-dwelling

cyanobacteria

(Coccochloris elebans, Oscillatoria sp.)

Sunlight

SALINITY, IN PERCENT

1850

1877

188918951903

1913

19581963

1966

196919721975

1978

19811984

1987

199019931996

1998

Railroad

causeway

constructed

Gunnison Bay

at Saline gage

(north part)

Gilbert Bay at

Boat Harbor gage

(south part)

Measurements

made in nonconsecutive years

1999

27

0

3

6

9

12

15

18

21

24

30

ity of 25 percent or higher; water south of the 

causeway (Gilbert Bay) has varied from about 6 

to 27 percent salinity. The Bear, Weber, 

and Jordan Rivers contribute about 

66 percent of the annual inflow of 2.9 

million acre-feet (one acre-foot equals 

325,851 gallons, or the amount of water 

that it would take to cover one acre to a 

depth of one foot) to the lake, precipitation into the lake contributes about 31 

percent, and ground-water inflow about 

3 percent. 

Water-budget studies done by the 

U.S. Geological Survey indicate that 

rivers contribute about 82 percent of 

the annual dissolved-solids load of 2.1 

million tons and springs contribute 18 

percent. Water can leave the lake only 

by evaporation, which amounts to about 

2.9 million acre-feet annually. The lake is saline 

because evaporation concentrates the dissolved 

salts in the remaining water. About 4.5 billion 

tons of salt are in the lake, and commercial 

removal of salt equals about 2.3 million tons 

annually. Sodium chloride (table salt) is the 

most common salt, although small amounts 

of other salts and elements also are present, 

including magnesium, potassium, sulfate, and 

carbonate. 

Five commercial enterprises extract salt 

and other minerals from the lake. Most use 

large solar evaporation ponds located near 

Stansbury Island and Bear River Bay to 

retrieve the salts.

Life in Great Salt Lake

Hypersaline lakes typically support fewer 

species of aquatic organisms than freshwater 

lakes because only a few specialized species 

can withstand the stress of saline water. The 

total number of species in Great Salt Lake 

depends on the salinity and is not accurately 

known because microscopic species have not 

been well studied. When the salinity is high 

(28 percent in Gunnison Bay), there may be 

as few as six species. At lower salinities (6 to 

9 percent in Gilbert Bay), the number of species has been estimated at 32. These organisms 

interact to form a complex and highly productive ecosystem. Algae (25 species reported 

in 1979) provide the base for the food chain 

through photosynthesis. They serve as food for 

brine shrimp and brine flies, which in turn are 

consumed by birds or by the shrimp harvested 

for the aquaculture industry. Bacteria, protozoa, and brine flies recycle the organic material 

to release nutrients and keep energy flowing 

through the system.

Union Pacific Railroad causeway viewed from 

Lakeside, Utah. Gunnison Bay on left, Gilbert 

Bay on right, January 1998.

Generalized ecosystem structure and energy flow 

within Gilbert Bay of Great Salt Lake.

Brine Shrimp

The invertebrate community 

of Great Salt Lake undergoes 

large annual variations in timing 

and abundance of life stages 

and is dominated by brine shrimp, Artemia 

franciscana. The variations are partly the result 

of changes in salinity, water temperature, 

nutrients, and algal populations. The young 

artemia, called nauplii, typically appear 

from over-wintering eggs (hard-walled cysts 

containing an embryo in dormancy) from late 

February to early March when water temperatures are between 32 and 41 degrees Fahrenheit. Their appearance follows the winter 

bloom of phytoplankton that provides food for 

the developing nauplii by about 1 month. Peak 

numbers of nauplii typically occur between 

mid-April and mid-May. The first generation 

of adults produced by the nauplii reproduces 

sexually and, if food availability and environmental conditions are suitable, will produce 

the second generation ovoviviparously (by live 

birth). If conditions are less favorable, oviparous reproduction produces cysts. Two or three 

generations of artemia are produced each year. 

The artemia graze the phytoplankton to near 

extinction by May. The lack of food causes 

adult females to begin oviparous cyst production. The maximum number of adults occurs 

about mid-May and then gradually declines 

until December, when water temperatures drop 

below about 37 degrees Fahrenheit and the 

adults die. 

Brine shrimp from Great Salt Lake have 

been commercially harvested as adults since 

1950 and as cysts since 1952. The annual 

harvest is regulated by the Utah Division of 

Wildlife Resources and begins October 1. The 

harvest lasts about 1 to 4 months, depending 

on the number of cysts available. The cysts are 

marketed worldwide and used extensively in 

aquaculture as a food source for larval stages 

of giant prawns and fish. Reported cyst harvest 

from 1964 to 1978 ranged from 83 tons in 

Average annual salinity of Great Salt Lake.
MUD

FLAT

MUD

FLATS

Miera Spit

W h i t e R o c k

B a y

B r i d g e r

B a y

Fremont Island Bar

Carrington

Bay

Gunnison

Island

Cub

Island

Tailings

Impoundment

Tailings

Impoundment

Gunnison Bay

215

184

80

201

36

171

111

138

108

37

98

53 126

39

68

84

193

15

68

186

89

80

80

15

15

15

15 84

102

89

89

89

134

69

83

91

83

98

MOUNTAINS

LAKESIDE

Badger

Island

Solar

Evaporation

Ponds

MUD FLAT

STANSBURYMOUNTAINS

SALT LAKE CO

TOOELE CO

DAVIS CO

BOX ELDER CO

TOOELE CO

WEBER CO

DAVIS CO

BOX ELDER CO

WEBER CO

H I L L A I R F O R C E R A N G E

Lakeside

MUD FLAT

Hill

Air

Force

Base

Egg

Island

Dolphin

Island

Promontory Point

Boat

Harbor

MUD FLAT

Blue Spring Hills

Black

Mountain

Spiral

Jetty

Hat Island

WMA

Solar

Evaporation Ponds

Boat Harbor

Visitor Center

Boat

Harbor

Locomotive

Springs WMA

Golden Spike National Historic Site

Salt Creek

WMA

Public Shooting

Grounds WMA

International

Airport

Salt Lake City

Ogden

Brigham

City

Tremonton

Saline

41°00'

41°30'

Great

Salt

Lake

Bear

River

Rive

W

r

eber

River

Jordan River

Weber

PROMONTORY

MOUNTAINS

Gilbert Bay

Farmington Bay

Railroad causeway

Fremont Island

Carrington

Island

Stansbury

Island

Willard Bay Bear

River

Bay

Canal

Surplus

Boat Harbor gage

Saline gage

Ogden

Willard Reservoir

Willard Bay

Upland Game

WMA

Ogden Bay WMA

Timpie

Springs

WMA

113°00' 112°00'

HANSEL

MOUNTAINS

WASATCH RANGE

Base from U.S. Geological Survey digital data, 1:100,000, 1978, 1979, 1980, 1984

Universal Transverse Mercator projection, zone 12

OQUIRRH

MOUNTAINS

0

0 10 20 KILOMETERS

10 20 MILES

Antelope

Island

Bear River

Migratory

Bird Refuge

Harold Crane WMA

Hat Island

Howard

Slough WMA

Farmington Bay WMA

Inland Sea

Shorebird Reserve

River

Gillmor Bird

Sanctuary

Willard Bay

State Park

The Nature Conservancy

Layton Wetlands

Preserve

Antelope

Island

State Park

CACHE CO

BOX ELDER CO

MUD FLAT

MUD FLAT

MUD FLAT

MUD FLAT

Solar

Evaporation Ponds

National

Forest

Great Salt Lake, altitude 4,200 feet

Intermittent water body

Utah State Park or National Monument

Waterfowl Management Area (WMA) or 

other wildlife reserve

EXPLANATION

USGS has measured lake altitude at or near Boat Harbor gage since 1875, and at Saline gage since 1966.

Great Salt Lake historic maximum altitude 4,211.60 feet, June 3, 1986, and April 1 and 15, 1987

Great Salt Lake historic minimum altitude 4,191.35 feet, October 15 and November 1, 1963

Gunnison Island WMA

Solar

Evaporation

Ponds

U T A H

Great

Salt

Lake
1966 to 265 pounds in 1968 to about 7,400 tons 

during 1995–96. (Reported amounts include 

total unprocessed biomass of which about 

half is cysts.) Historically, salinity of the lake 

has been the major factor associated with the 

abundance and distribution of artemia and the 

success of the cyst harvest. When salinity of 

Gilbert Bay varied from 6 to 10 percent from 

1982 to 1989, cyst production was poor and 

most harvesters moved to Gunnison Bay, the 

north part of the lake, where the salinity was 

15 to 17 percent. Since about 1990, reproducing populations of artemia have been limited 

to Gilbert Bay, although during the 1998–99 

season limited harvest efforts resumed in Gunnison Bay.

Brine Flies

Two species of brine 

flies (or ephydra) live in the lake. Adult flies 

congregate along the shoreline for breeding and 

occasionally reach densities of 370 million per 

mile of beach. Although they do not bite, they 

often land on people and may be annoying. 

The larval form of the brine fly (shown above 

at twice lifesize) feeds on detritus and benthic 

algae and plays an important role in recycling 

nutrients within the lake.

Migratory Birds

Great Salt Lake supports from 2 to 5 million 

shorebirds, as many 

as 1.7 million Eared 

Grebes, and hundreds of 

thousands of waterfowl 

during spring and fall migration. Because of 

its importance to migratory birds, the lake was 

designated a part of the Western Hemisphere 

Shorebird Reserve Network in 1992. The lake 

is a major staging area for some shorebirds, 

such as the Wilson’s Phalarope. In July 1986, 

387,000 Wilson’s Phalarope were estimated in a 

1-day aerial survey, and 600,000 were estimated 

on a single day in July 1991. Studies indicate 

that at least 5,000 to 10,000 Snowy Plovers nest 

on the alkaline flats surrounding the lake. The 

current estimate for breeding American Avocets 

is 40,000 and for Black-necked Stilts 30,000. 

Hundreds of thousands of Eared Grebes stage 

on the lake, fattening on the abundant brine 

shrimp. One of the world’s largest populations 

of White-faced Ibis nests in the marshes along 

the east side of the lake. The lake hosts the largest number of breeding California Gulls, includCommercial shrimp-harvesting craft with isolation boom 

suspended by orange floats.

ing the world’s largest recorded single 

colony. About 150,000 breeding adults 

have been counted in recent years. The 

American White Pelican colony on 

Gunnison Island ranks among the three 

largest colonies in North America.

The lake and its marshes provide a 

resting and staging area for the birds as 

well as an abundance of brine shrimp 

and brine flies that serve as food. 

Important wetlands include Bear River 

Migratory Bird Refuge operated by 

the U.S. Fish and Wildlife Service; 

Locomotive Springs, Salt Creek, Public 

Shooting Grounds, Harold Crane, Willard Bay Upland Game, Ogden Bay, 

Howard Slough, Farmington Bay, and 

Timpie Springs Waterfowl Management Areas operated by the Utah Division of 

Wildlife Resources; Layton Wetlands Preserve 

managed by the Nature Conservancy; Gillmor Bird Sanctuary managed by the Audubon 

Society; and the Inland Sea Shorebird Reserve 

managed by Kennecott Utah Copper. Most of 

these areas are accessible seasonally for bird 

watching and some for duck hunting.

Recreation

Motor boating is not popular on the lake 

because of corrosion problems; however, two 

marinas provide facilities for sailing: Great 

Salt Lake Marina on the south end of the lake 

and Antelope Island State Park on Antelope 

Island. The more popular of the marinas and 

headquarters for the Great Salt Lake Yacht Club 

is located at the south end of the lake where 

launching is free but facilities are limited to a 

boat ramp, picnic area, and restrooms. Freshwater boating is available at Willard Reservoir, 

east of Bear River Bay, and camping facilities are available at Willard Bay State Park. A 

commercial business operates daily boat trips 

on the lake from Great Salt Lake Marina in the 

summer. A per-vehicle fee for use of the Davis 

County Causeway and Antelope Island State 

Park provides access to a boat ramp, restrooms, 

showers, picnic areas, camping areas (by reservation only), an excellent visitor center, miles 

of horse and bike trails, a resident bison herd, 

and a café.

Golden Spike National Historic Site marks 

the spot where the last spike in the transcontinental railroad was driven on May 10, 1869. 

Facilities include a visitor center, historic locomotives, and interpretive presentations. 

Antelope Island, with an area of about 

28,000 acres, is the largest of the islands in 

Great Salt Lake and is publicly owned and 

accessible by vehicle. Carrington and Fremont 

Islands, although relatively large, are accessible 

only by boat and are privately owned. Gunnison 

and Hat Islands are protected as bird rookeries 

and have no public access. Stansbury Island is 

accessible by vehicle but is mostly privately 

owned.

Bird watching is seasonally popular at most 

of the wetlands along the east shore. There is no 

charge for access to State Waterfowl Management Areas. Duck and goose hunting is allowed 

(with purchased permits) in the fall at all of the 

State Waterfowl Management Areas.

Additional References

Arnow, Ted, and Stephens, Doyle, 1990, Hydrologic characteristics of the Great Salt Lake, 

Utah: 1847–1986: U.S. Geological Survey 

Water-Supply Paper 2332, 32 p.

Curry, D.R., Atwood, G., and Mabey, D.R. 

1984. Major levels of Great Salt Lake and 

Lake Bonneville: Map 73, Utah Geological 

and Mineral Survey. 

Gwynn, J.W., ed., 1980, Great Salt Lake, A 

scientific, historical, and economic overview: 

Utah Geological and Mineral Survey Bulletin 

116, 400 p.

Morgan, D.L., 1947, The Great Salt Lake: Salt 

Lake City, University of Utah Press, 432 p.

Stephens, D.W., 1998, Salinity-induced changes 

in the aquatic ecosystem of Great Salt Lake, 

Utah: 1–7, in J. Pitman and A. Carroll, eds., 

Modern and Ancient Lake Systems, Utah 

Geological Survey Guidebook 26.

— By Doyle W. Stephens and Joe Gardner

Contact Information:

Antelope Island State Park 801-721-9569

Entrance station 801-773-2941

Bear River Migratory Bird Refuge 435-723-5887

Friends of Great Salt Lake 801-583-5593

Website www.fogsl.org

Great Salt Lake Marina, near Saltair 801-250-1898 

Golden Spike National Historic Site 435-471-2209

Great Salt Lake Yacht Club www.gslyc.org

Inland Sea Shorebird Reserve Website

 www.kennecott.com/SD_env_wetlands.html

The Nature Conservancy of Utah

Layton Wetlands Preserve 801-531-0999

Website www.nature.org/utah/

Salt Island Adventures (boat cruises) 801-252-9336

Utah Division of Wildlife Resources 801-538-4700

Website wildlife.utah.gov/index.php

Willard Bay State Park 435-734-9494

This information is provided by the U.S. 

Geological Survey, which has been researching 

Great Salt Lake since the G.C. Gilbert exploration of the 1870s. For additional information 

about Great Salt Lake see our web site at:

http://ut.water.usgs.gov/

Information on technical reports and hydrologic data of Great Salt Lake can be obtained 

from:

U.S. Geological Survey

2329 Orton Circle

Salt Lake City, Utah 84119-2047

Phone (801) 908-5000