what is the name of spain's longest river?

The longest river entirely within Spain is the Ebro River, which is about 930 kilometers (approximately 578 miles) long. It starts in the Cantabrian Mountains at Fontibre and flows eastward into the Mediterranean Sea. Although the Tagus River is longer overall, stretching about 1,007 kilometers, part of it flows outside Spain, into Portugal. Thus, the Ebro is the longest river flowing fully through Spain.