In the case of rivers such as the Colorado, the length listed in the table below is solely that of the main stem.
[1] In the case of the Grijalva and Usumacinta, it is the combined lengths of two river systems that share a delta.
[2] In the case of the Nazas and Aguanaval, it is the combined lengths of separate rivers that flow into the same closed basin.
The Colorado and the Rio Grande (Río Bravo del Norte or Río Bravo) begin in the United States and flow into Mexico, while the Usumacinta begins in Guatemala and flows into Mexico.
[3][4] The primary source for the length, watershed, and surface runoff data in the table below is the 10th edition of Statistics on Water in Mexico, published by the National Water Commission in Mexico (CONAGUA); exceptions are as noted.