On Thursday, the Netherlands marks the 75th anniversary of the completion of the Afsluitdijk, the country's longest dike, which keeps the North Sea at bay. It protects the country's biggest freshwater lake and source of drinking water.

Water is a real threat to the Netherlands, two-thirds of which lies below sea level. Fears that huge waves could flood the country increased after the 2004 Indian Ocean tsunami that left some 230,000 people dead or missing, Vos said.

Rising sea levels due to global warming have also added to concerns. Memories of the 1953 flood when a massive North Sea storm breached the country's dikes and resulted in about 1,800 deaths still linger.

Vos said proposals to strengthen the Afsluitdijk by 2020, which stands about 7.5 metres above sea level, include raising its height, widening the barrier which now extends to 125 metres in some places, and building more sluice gates to improve water flow control.

"There is also a suggestion to plant artificial grass on the dike," he said.