2025-08-08

Harbour storiesNatureMaritime & Nautical

Does salt water enter the Scheldt at high tide?

Do you have a question about the port? Submit your question and we will find the answer for you. For example, Joop wondered whether salt water flows into the Scheldt at high tide. 

The answer: YES!

Yves Plancke is a research engineer at Port of Antwerp-Bruges and the ideal person to give us some more explanation: "It is indeed true that salt water flows into the Scheldt estuary at high tide. In an estuary, the sea’s salt water merges with the river’s fresh water. The two mix together. As a result, salinity levels in the Scheldt fluctuate across a range of tens of kilometres. The estuary contains salt water at the sea end, fresh water upstream, and brackish water in between."

The green bank of the Galgenschoor in the port of Antwerp.

Seasonal variations

Salinity fluctuates annually,and in winter, river discharge lowers salt levels, resulting in brackish water extending to roughly 60 km, near the Belgian-Dutch border. Following a dry summer, brackish water extends once more up to about the mouth of the Durme, some 110 km inland.

Map showing the Belgian-Dutch border, Antwerp and the mouth of the Durme.

A unique habitat of mudflats and salt marshes

The natural combination of fresh and salt water creates unique flora and fauna: the mud flats and salt marshes of the Scheldt region. Twice a day, the tides flood these areas before they dry out again. Examples include the flooded land of Saeftinghe, the Galgenschoor nature reserve, and Sint-Anneke beach. The area hosts plants that thrive in brackish water, as well as fish, invertebrates, and minute benthic species, which attract birds.

A ship sails past the green Saefthinghe area where we see small streams running through the greenery.©Saefthinghe

Does salt or fresh water also have an impact on shipping?

Yves: "Because salt water is denser , ships can shift their position by up to ten centimetres when transitioning to fresh water. At present, our sailing plans do not consider the influence of salt on draught. Rijkswaterstaat (Netherlands) and the Hydraulic Laboratory (Belgium) do carry out ongoing salinity measurements at several sites along the estuary. We use this data to monitor the state of the ecosystem."

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A hand gliding along the water of the Scheldt river.

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