Hundreds of purpose-built waterways which allow fish to bypass dams, pumping stations and sluices are proving a great success, Trouw reports on Monday.

As soon as the special routes are opened, migrating fish stream through in large numbers, Trouw says, quoting research by civil engineering bureau Arcadis.

Fish such as salmon, sturgeon and gudgeon had almost disappeared from the Netherlands’ waterways because of a combination of measures to drain land and poor water quality.

But improved river quality, thanks to international agreements, has led to an increase in numbers, and fewer bottlenecks along popular migration routes.

A 2008 report indentified 2,600 obstacles, of which around half have now been bypassed, Trouw says.