Possible Clues:

• River of NE Spain
• Spanish runner featuring in outside broadcast
• River that divided the Romans and the Carthaginians
• River that runs through 23-Across
• Longest river entirely within Spanish borders
• Second-longest river in Iberia
• River that rises in the Cantabrian Mountains
• River of northern Spain
• Spanish river's swirling bore
• River of Zaragoza