Blies River

The Blies is an almost 100 km long right tributary of the Saar in the German Saarland and in the French Lorraine (Département Moselle) and crosses several natural areas on its course from the north-east of the Saarland in the district of St. Wendel to the southern tip of the country.With a water flow of 20.7 m³/s at the mouth, the Blies is not only the largest tributary of the Saar, but hydrologically even its main source of pressure, since the Saar is slightly smaller at this point with an average discharge of 19.0 m³/s. With 1889 of 3673 square kilometers, the Blies takes up just over half of the total catchment area at the mouth.Source: de.wikipedia.org/wiki/Blies

At almost a hundred kilometers, the Blies is a tributary of the Saar.