The expansion of the Saar between its confluence with the Moselle near Konz and Saarbrücken was carried out on the basis of an administrative agreement dated March 28, 1974, between the Federal Republic of Germany, Saarland, and Rhineland-Palatinate. The goal was to make the Saar navigable for the Europaschiff (1,350 t, Class IV waterway) and for pushed barges with a carrying capacity of up to 3,300 t. The expansion served to connect the entire economic area in the Saar Valley and the West Palatinate to the European waterway network and, above all, to improve the location of the Saarland mining industry. Previously, the only connection to the French canal system via the upper reaches of the Saar (Saar Coal Canal) existed for vessels with a carrying capacity of 300 t.
The Saar has a height difference of 55 m between the Trier (Moselle) barrage and the existing Saarbrücken barrage. This difference is now overcome by six barrages.
Expansion work began in 1976, and the first section between the estuary and Dillingen was completed in early 1987. The connection to the Dillinger Hütte waterway network enables the Saarland steelworks to be supplied with iron ore from overseas by water at the most cost-effective rate.
The Mettlach barrage (river km 31.2) is the second highest barrage at 11.00 m. It is equipped with two lock chambers (190 m x 12 m, 40 m x 12.75 m), three weir segments, and two turbines (2 x 2900 kW), as well as two generator sets with an installed capacity of 3900 kVA.