Natural sweet-salty transition

Until 1969, Lauwersmeer was still known as Lauwerszee. For water safety reasons, the lake was closed off from the Wadden Sea and became a freshwater lake, which had negative consequences for vegetation, fish, and birds. Fish, for example, need brackish water to adapt to changing salinity levels. A natural transition between salt and freshwater is important for fish migration. 

Improving water quality and biodiversity
Nowadays, drastic closure for safety reasons is no longer necessary. It is technically feasible to allow more salt into the northern part of Lauwersmeer for a better transition to the fresh water in the southern part of the lake. We want to strengthen the natural transition between fresh and salt water so that water quality improves. This is good for fish migration and biodiversity. 

Fresh water for agriculture
At the same time, farmers around Lauwersmeer need fresh water for agriculture and their livestock. The agricultural land is mainly located on the south side of the lake. Nature and agricultural interests can coexist if we make the northern part of the lake brackish and keep the southern part fresh.

In the Wadden Sea region, there are hardly any places left where fresh river water can mix with salt sea water. The lack of these kinds of transitions is one reason why the underwater nature of the Wadden Sea is not doing well at present. Fresh and salt water once flowed together in the former Lauwerszee. Migratory fish swam in to spawn and grow. This is now hardly possible due to the closure of the lake. 

Fish migration
We want to restore this migration and nursery function. To do so, nature needs a freshwater-saltwater connection with a brackish transitional environment. This brackish water allows fish to gradually adapt to increasingly salty conditions. Conversely, they use the brackish zone to acclimatize to increasingly fresh water. In addition, a more natural transition between fresh and salt water also offers opportunities for other plants and animals. Restoration can have an effect on all underwater life, right down to the capillaries of Drenthe and Frisian streams. 

A more open connection between the Wadden Sea and the Lauwerskust area will create more space for the water and allow the area to grow in a more natural way as sea levels rise. Naturally, water safety is paramount in this regard.

We want to be able to accurately determine the salt content in and around Lauwersmeer. That is why we have started constructing a chloride monitoring network. In 2025 and 2026, around 50 measuring points will be installed in the lake and in nature and agricultural areas. This will enable the salt content to be measured daily at different locations and depths. In this way, together with our regional partners, we will learn more about fresh and salt water in the area. 

What exactly are we measuring?
Although the project is known as a 'saltwater monitoring network', the sensors actually measure the electrical conductivity (EC) of the water. In general, the higher the EC, the more ions there are, and therefore the saltier the water.

Read more about the saltwater monitoring network. 

There are already a number of saltwater measuring points. We will be adding around 50 more measuring points in 2025 and 2026. Based on this, we will create a data model that will help us map the freshwater-saltwater dynamics of the lake. The model will also enable us to map the effects of future measures.  

More diverse data
More and better data is needed on the salt and freshwater dynamics in Lauwersmeer. We need data under different conditions (e.g., different depths and seasons). Based on this data, we will soon be able to control the inflow of salt water. We expect this to keep the chloride content in and around the lake within the desired range. We will include analyses of the measurement results in our exploration of the best solution for a freshwater-saltwater transition. This exploration will continue until 2028. 

We are already managing both fresh and salt water, but we want to be able to do this more accurately. That is why we are setting up a saltwater monitoring network. We are also exploring the best solution for a more natural transition between fresh and salt water.

Enough fresh water
In the northern part of Lauwersmeer, we want to let in controlled salt water. We do this via the R.J. Cleveringsluizen. The southern part of the lake must remain fresh. We ensure this by means of a constant 'fresh inflow' from rivers and canals in Friesland, Groningen, and Drenthe. During dry periods, fresh water is supplied from the IJsselmeer, using inlets, pumping stations, and weirs. This allows us to maintain water levels and prevent salinization of the surface water. 

To measure is to know
We will soon be able to accurately measure the salinity of the water using a saltwater monitoring network. If necessary, immediate action can then be taken. For example, by closing the locks and supplying more fresh water from the hinterland. 
 

Salt water is heavier than fresh water because salt water has a higher density than fresh water. Naturally, salt water therefore tends to form a layer beneath the layer of fresh water. 

Salinization in the Netherlands is mainly caused by intruding seawater and brackish groundwater rising to the surface (salt seepage). This causes it to end up in the soil, groundwater, and surface water. We believe that salinization in the Lauwersmeer area is increasing due to rising sea levels and soil subsidence.

We want to achieve a good balance between saltwater and freshwater. During droughts, freshwater is scarce and we may have to prevent saltwater from entering the lake for a while. At other times, there is enough rain and you can allow extra saltwater to enter. 

For nature restoration (biodiversity, fish migration, improvement of water quality), it is necessary for the northern part of the lake to become more brackish. To this end, we will allow controlled saltwater into Lauwersmeer. With the help of the saltwater measuring system, we want to prevent excessive salt intrusion. In addition, we will ensure that sufficient fresh water is supplied via rivers and the IJsselmeer to counteract the salt seepage.

The water board regularly checks whether the water system still provides adequate protection against flooding. Climate change can alter conditions: there is more rainfall and sea levels are rising. Lauwersmeer plays an important role in this system and helps to safely drain water to the Wadden Sea.

In order to remain well protected in the future, Lauwersmeer must be able to continue to drain sufficient water. There are various ways of achieving this. One of the ideas is to build a pumping station at Lauwersoog. But there are still many choices to be made: which solutions are most suitable, which combinations are possible, and when should we implement certain measures?

In the exploratory phase of the PAGW (Programma Aanpak Grote Wateren, Program for Tackling Large Waterways) Future-Proof Lauwersmeer project, we are investigating how we can improve the connection between fresh and salt water, with water safety as a prerequisite.