Natural freshwater-saltwater transition

Until 1969, Lauwersmeer was still known as the Lauwers sea. 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. For example, fish need brackish water to adapt to changing salinity levels. A natural transition between saltwater and freshwater is important for fish migration. 

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

Freshwater for agriculture
At the same time, farmers around Lauwersmeer need freshwater for agriculture and their livestock. The agricultural land is mainly located on the southern 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 seawater. The lack of these kinds of transitions is one reason why the aquatic nature of the Wadden Sea is not doing well at present. Freshwater and saltwater once flowed together in the former Lauwers sea. 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 acclimatise to increasingly fresh water. In addition, a more natural transition between freshwater and saltwater also offers opportunities for other plants and animals. Restoration can have an effect on all aquatic life, right down to the capillary streams in Drenthe and Friesland. 

A more open connection between the Wadden Sea and the Lauwers coastal 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 determine the salt content in and around lake Lauwersmeer with accuracy. That is why we have started constructing a chloride measuring 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. This will help us, and our regional partners, to learn more about freshwater and saltwater 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 saltwater and freshwater dynamics in lake 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 saltwater. We expect this to keep the chloride content in and around the lake within the required range. We will include analyses of the measurement results in our exploration of the best solution for a freshwater-saltwater transition. This exploratory study will continue until 2028. 

We are already managing both freshwater and saltwater, 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 freshwater and saltwater.

Enough freshwater
We want to control the entry of saltwater in the northern part of lake Lauwersmeer with the R.J. Clevering locks. The southern part of the lake must remain freshwater. We ensure this by means of a constant 'freshwater inflow' from rivers and canals in Friesland, Groningen, and Drenthe. During dry periods, freshwater is supplied from lake IJsselmeer, using inlets, pumping stations, and weirs. This allows us to maintain water levels and prevent salinisation of the surface water. 

To measure is to know
We will soon be able to measure the salinity of the water accurately with a saltwater monitoring network. It means that action can be taken immediately if necessary. For example, by closing the locks and supplying more freshwater from the hinterland. 
 

Saltwater is heavier than freshwater because saltwater has a higher density than freshwater. Naturally, saltwater tends to form a layer beneath the layer of freshwater. 

Salinisation 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 salinisation in the lake Lauwersmeer area is increasing due to rising sea levels and 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 saltwater into lake Lauwersmeer in a controlled manner. With the help of the saltwater monitoring system, we want to prevent excessive salt intrusion. In addition, we will ensure that sufficient freshwater is supplied via rivers and lake IJsselmeer to counteract the salt seepage.

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

In order to remain well protected in the future, lake Lauwersmeer must be able to continue to drain enough 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 (Programmatic Approach to Large Water Bodies) Future-Proof lake Lauwersmeer project, we are studying how we can improve the connection between freshwater and saltwater, with water safety as a prerequisite.