Includes the extreme northwestern corner of Iowa, the entire Floyd River basin, and part of the Big Sioux River basin. Bounded on east and south by the Little Sioux River basin.

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

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