The woods Kralingse Bos, with the lake Kralingse Plas in it, is one of the largest green recreational areas of Rotterdam. Until 2010, the lake’s water regularly failed to meet the European standards for bathing water. It was not only slightly contaminated with lead from the factories that were located there until the beginning of the last century, there were also too many nutrients in the water. These nutrients encourage algae growth and thus result in a limited and uniform stock. The fish ladder is part of a comprehensive programme of measures to improve the lake’s water quality. In addition to adjustments to the banks, the lake was partially dredged and a dephosphatation installation was placed, as well as a pumping station that fish can pass through. The fish ladder between the Kralingse Plas and the higher water bodies is also part of this programme. This ladder allows a natural migration to a higher spawning ground in the so-called Wolvenvallei (Wolf Valley). To bridge the 120-centimetre difference in height, a series of 10-centimetre waterfalls were created. The vegetation on the banks ensures that the fish are sheltered during their migration. Everybody wins: the fish now have a better habitat and the residents of Rotterdam can go and have a swim.
-Rotterdam (NL) 2010
-Hoogheemraadschap van Schieland en de Krimpenerwaard, Gemeete (Municipality of Rotterdam
more info: talk by parkmanager