The Netherlands has turned 37.2 million tonnes of dredged lakebed sediment into a chain of artificial islands designed to restore wildlife habitats and improve the ecosystem of Markermeer lake.
Since 2016, engineers and conservationists have used sand, clay, silt and peat removed from the lakebed to create Marker Wadden, an archipelago of seven artificial islands and surrounding underwater habitats covering about 1,300 hectares.
The project aims to address ecological problems that developed in Markermeer after decades of water engineering. The lake was separated from the former Zuiderzee through the construction of dams, creating a freshwater basin with limited natural connections between land and water.
Over time, large quantities of fine sediment accumulated on the lakebed. Strong winds frequently stirred the silt, reducing water clarity and limiting sunlight available for aquatic plants.
Instead of treating the sediment as waste, the project used it as the building material for new islands, shallow waters and sheltered habitats.
How the artificial islands were built
Engineers created rings of sand on the lakebed and filled them with muddy water. The clay, silt and peat gradually settled inside the enclosures, forming the foundations of the islands.
The process has not been completely predictable. The newly deposited sediment compacted and settled more than expected, requiring additional material in some areas. Erosion has also reshaped parts of the islands, meaning the landscape continues to change and requires monitoring.
Wildlife begins using the new habitats
Birds were among the first animals to take advantage of the newly created landscape. As vegetation developed, the number of bird species using the islands increased.
Monitoring recorded 47 breeding bird species by 2021, while more than 60,000 migratory birds had used the islands for food or shelter during the year to July.
Greater flamingos, Eurasian spoonbills and gull billed terns were among the birds recorded at Marker Wadden. Researchers also observed fish using the sheltered waters around the islands.
Surveys conducted in 2018 and 2019 recorded 19 fish species in monitored areas, including evidence of spawning and fish larvae in vegetated shallow waters. The developing ecosystem has also attracted phytoplankton, zooplankton, insects, spiders and molluscs.
Challenges remain
The artificial islands have also faced several ecological and engineering challenges. Willow trees have spread into areas intended to develop as reedbeds, while the managed water levels of Markermeer can make it difficult to reproduce the seasonal conditions that naturally encourage reed growth.
Erosion has affected some beaches as well. One northern beach disappeared in 2020 and was later replenished with fresh sand.
Researchers have reported clearer water several kilometres downwind of Marker Wadden, but the full impact of the project on the wider lake remains uncertain.
Markermeer covers approximately 70,000 hectares, meaning the 1,300 hectare Marker Wadden project represents only a small part of the overall lake. The 1,300 hectare figure also includes surrounding underwater habitats rather than representing 1,300 hectares of newly emerged land.
New model for nature restoration
Marker Wadden is not designed to recreate the lake exactly as it existed before human intervention. Instead, the project creates new physical conditions and allows natural processes to determine how the ecosystem develops.
The experiment demonstrates how dredged sediment which is often treated as waste, can be repurposed to create habitats for wildlife.
Although its long term effect on the wider Markermeer ecosystem is still being studied, the project has already attracted numerous bird and fish species and created new aquatic food webs.
The Dutch experiment shows how material removed during infrastructure and water management projects could potentially be reused to support ecological restoration rather than simply being discarded.