Extends from near the center of the state to the Mississippi River in Southeastern Iowa.

Includes the Iowa portion of the Little Sioux River drainage area, all of the drainage areas of the Soldier and Boyer Rivers, and a number of smaller streams which are tributaries to the Missouri River.

Includes the Iowa portion of the Upper Iowa and Wapsipinicon River drainage areas, all the drainage areas of the Yellow, Turkey, and Maquoketa rivers, and intermediate areas between these river basins which drain directly to the Mississippi River through a number of minor streams.

Extends across east-central Iowa from beyond the state line on the north to the Mississippi River on the southeast. Bounded almost entirely by the Wapsipinicon River basin on the east and by the Des Moines River and Skunk River basins on the west.

Includes the Iowa portion of the drainage area of the Nodaway, Platte, Grand, Chariton, Fabius, Wyaconda, and Fox rivers and Tarkio Creek.