The great plains
According to google "The Great Plains is the broad expanse of flat land, much of it covered in prairie, steppe, and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U.S. and Canada"
The Great Plains - hope this helps
Great Lakes pollution
In 1972 and 2002, Canada and the U.S. agreed to take action regarding Great Lakes pollution.