Region
United States
2,820
Colorado
487
Developing countries
79
California
65
India
59
China
58
Africa
36
Iowa
32
Mexico
31
Minnesota
27
Southern States
27
West (U.S.)
27
Pennsylvania
24
Wisconsin
24
Canada
23
European Union countries
23
Africa, Sub-Saharan
21
Great Britain
20
Japan
20
North America
20
Tropics
20
Kansas
19
Europe
18
Brazil
17
Middle West
17
Arizona
15
Soviet Union
15
European Economic Community countries
14
Florida
14
Great Plains
14
Nebraska
14
Asia
13
Montana
13
North Dakota
12
Oregon
12
Russia (Federation)
12
Texas
12
Wyoming
12
New Mexico
11
Australia
10
Conestoga River Watershed
10
Egypt
10
Europe, Eastern
10
Maryland
10
South Dakota
10
Georgia
9
Illinois
9
North Carolina
9
Asia, Central
8
Chesapeake Bay Watershed
8
more ...