Key Terms
(Definitions from Merriam Webster):
interlocking system (of rivers) - rivers connected to each other.
(Definitions from Merriam Webster):
interlocking system (of rivers) - rivers connected to each other.

(Source: "Online Photo Museum"; Steamboats.com Virtual Online Museum)
Interlocking system (of rivers):
The Upper Mississippi River System is a 1,300-mile waterway linking five states to the Gulf Coast export markets; this River System provides a tremendous range of usage such as commercial navigation, recreation, and fish and wildlife. In that region, there are more than 30 million residents whom depend on a river water for public and industrial supplies, power plant cooling, waste water assimilation, and other uses.
The Upper Mississippi River System is a 1,300-mile waterway linking five states to the Gulf Coast export markets; this River System provides a tremendous range of usage such as commercial navigation, recreation, and fish and wildlife. In that region, there are more than 30 million residents whom depend on a river water for public and industrial supplies, power plant cooling, waste water assimilation, and other uses.