Natural Features
Resacas Are Old River Channels That Shape Life in the Valley
Resacas are the curved, oxbow-shaped lakes left behind when the Rio Grande shifted course—they provide wildlife habitat but also carry flood risk.
As the Rio Grande moved over hundreds of years, it left behind curved water bodies called resacas. These are old sections of the river that got cut off when the river changed course. They look like crescent-shaped lakes.
Many resacas in urban areas are kept full by pumping systems, but rural resacas are often dry or marshy except in rainy weather. They support fish, birds, and alligators. You will find them spread across the flat landscape of Hidalgo County.
Resacas can also cause flooding. They fill up fast during heavy rain and drain slowly. If you are buying property near one, check its flood zone status at the FEMA Flood Map Service Center. Also ask whether the property falls inside a drainage district—that district may have rules about what you can build nearby.
Source to confirm: Handbook of Texas – Resacas