& Nature
When it was constructed in 1932, the Afsluitdijk was a stunning piece of hydraulic engineering, but eventually it had major consequences on nature.
Ecologists consider the Afsluitdijk, along with the Delta Works, the biggest natural catastrophe in Dutch history. In the IJsselmeer area, fish and bird populations have severely declined, as has the quality of the water.
Which effect did the Afsluitdijk have on nature?
Voor de aanleg van de Afsluitdijk was de Zuiderzee een estuarium, een schakel tussen de zee en de rivieren. De rivieren gingen geleidelijk over in de zee wat zorgde voor een variatie aan leefgebieden en een grote voedselproductiviteit. Het was een overvloedig visgebied met meer dan vijftig soorten, een kraamkamer voor vis en een eldorado voor vogels.
Na de aanleg van de Afsluitdijk verzoette het water in het IJsselmeer binnen enkele maanden. De dynamiek in het gebied verdween, het waterpeil werd streng gereguleerd en de dijk blokkeerde de trekroutes van miljoenen vissen. Harde dijken en een onnatuurlijk peilbeheer – laag in de winter en hoog in de zomer – zorgden ervoor dat er onvoldoende geleidelijke overgangen zijn tussen land- en water. Juist in die ondiepe gebieden paaien vissen en vinden vogels hun voedsel.
A highway for fish
The Afsluitdijk is an ecological barrier between two internationally important nature areas: the IJsselmeer and the Wadden Sea. Underwater, migrating fish literally bump their noses against the concrete. A four-kilometre-long river is now being constructed right through the dyke, through which fish can migrate. From the salty Wadden Sea to the fresh IJsselmeer. And back again, because migratory fish need fresh and salt water to grow and reproduce.
25,000 kilometres of river to be made free-flowing for migratory fish by 2030 Biodiversity Strategy, European Union
Why is it so important? Migratory fish are seriously endangered species. Globally, their population has shrunk by 76 percent, the biodiversity in rivers is deteriorating twice as fast as in the woods or the ocean, and river fish of over thirty kilogrammes are well-nigh extinct. This is shown by an international study of the World Fish Migration Foundation and the WWF. The most effective way to restore fish populations and biodiversity is by removing dams, according to the conservation organisations.
A well-known migratory fish is the eel, that for reproductive purposes must swim from Volendam to the Sargasso Sea (six thousand kilometres) before swimming all the way back as tiny elvers. Other migratory fish include smelt, houting, salmon, weever, sea trout and three-spined stickleback. Migratory fish are important for nature. Especially young fish serve as food for other endangered species like porpoise, dolphin and various birds. So, without sticklebacks no spoonbills and without smelt no black tern or grebe.
How it works: Migratory fish will not have any difficulties finding the Fish Migration River. They follow the smell of the fresh or salt water. Strong swimmers like salmon and sea lamprey swim to the other side independently. Weaker swimmers or young fish can be carried by the tide. The river connects to ‘swimways’, a kind of highways for fish formed by deep channels in the bottom of the Wadden Sea or Lake IJsselmeer.
New beginnings
‘Climate adaptation is an opportunity for nature’
Soon, millions of fish will use the Fish Migration River to swim into Lake IJsselmeer. What is the quality of nature in their new habitat? Five questions to Flos Fleischer, director of Blauwe Hart Natuurlijk, a coalition dedicated to a vital and healthy IJsselmeer area.
What is the current quality of nature in the IJsselmeer region?
‘Lake IJsselmeer is the largest freshwater lake in Europe. A unique ecosystem, but it’s under serious pressure. We will not reach the so-called conservation objectives set for Natura-2000 sites. The main reason is a lack of habitats of sufficient quality and size.'
What does it need to recover?
‘We need areas that increase the productivity, the food supply. From water plants and animals to the fish that an osprey lifts from the water. It is the underwater part of an artificial lake that is difficult to activate. Due to land reclamations and dykes, the banks are hard and the water level is strictly regulated. This is unfavourable for nature. A lake area should be a breathing system that floods when there’s a lot of water and runs dry in drier periods. When water recedes, it takes nutrients with it. To provide fish and birds with a proper habitat, we have to bring back reed beds and shallow and brackish zones.’
‘The Fish Migration River is a first step in improving the ecological system as a whole’ Flos Fleischer,
Blauwe Hart Natuurlijk
Which role does the Fish Migration River play in this nature restoration?
‘The Fish Migration River enables fish to migrate 24/7. This is an improvement. But it turned out to be a very technical solution. Different from what we expected. In the preliminary phase, we said: If you reinforce the Afsluitdijk, you have to give the fish a good front- and backyard. To me, a solid stone basin does not fulfil the expectation.’
What could have been done?
‘They could have gotten more from it. Now, only a passage has been made, no swamp or new habitats that would ensure an added ecological value on a larger scale. I consider the Fish Migration River a first step in improving the entire ecological system. It obliges us to look further: What do the fish end up in? Where do they go? Can they swim on, or do they come up against something again? It’s a learning curve. In a new project on the Den Oever side, we’re already taking it a step further by putting in shallows, reed beds, riparian zones and fish passages across a larger area and in a natural way.’
Do people listen to ecologists in large infrastructural projects?
‘Climate adaptation offers nature a chance, making effective collaboration with ecologists crucial. For the Afsluitdijk, we had a good preliminary phase. Nature organisations could submit several points of improvement, which were accepted. But then the contract meetings take place, and not a single ecologist is at the table. Only legal experts. They discuss issues like time, money and risk factors, and things go off the table. For example, we forcefully pleaded to not make the causeway too high. But push came to shove and now the dyke is steeper than before. To make it less steep, extra permits had to be applied for. For nature, the easy way is not the best solution. Now, certain bird species can’t forage properly.’
From a fish-eye view
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