For many decades the Moselle and Saar have been developed as major shipping routes, and the 28 locks on the Moselle and 6 on the Saar present barriers to fish migration. Inland waterway transport plays an important role in the movement of goods in Europe, with more than 4,000 km of navigable waterways. Thus, these major and long-established civil engineering works, in existence for many decades, mean that the original, natural state of the rivers probably cannot be known.