The Arroyo Colorado lies in Willacy, Cameron, and Hidalgo Counties and is the major drainage channel for the two dozen cities in this area, with the notable exception of Brownsville. Almost 500,000 acres in the three counties are irrigated for cotton, citrus, vegetables, grain sorghum, corn, and sugar cane production. At the lower end of the watershed, the 45,000-acre Laguna Atascosa National Wildlife Refuge forms the largest natural habitat left in this area.
South Bay is a virtually unimpacted area at the southern end of the laguna.
For Segment 2202, concerns identified are for nitrogen and phosphorus. Due to elevated levels of fecal coliform bacteria, contact recreation use is not supported. For Segment 2201, concerns identified are for dissolved oxygen, nitrogen, and phosphorus compounds. The land bridge dividing the Laguna Madre is near the northern border of Willacy County. The lower Laguna Madre receives runoff from land in Cameron, Willacy, and Hidalgo Counties primarily by way of the Arroyo Colorado.