Princess Irene locks Wijk bij Duurstede - Wijk bij Duurstede

If you stop for a moment at the Prinses Irenesluizen, you can see four semi-circular basins in the landscape in the distance. These are popularly known as 'Thijsse's Eggs', because of their shape, and named after their creator Jo Thijsse. Crossing the canal and the river posed a number of problems, including a side current that changed a ship's course. Another problem was that the canal was one metre deeper than the bottom of the river.

Furthermore, flowing water along a widening causes a 'down', which provides an extra tricky flow for navigation and can cause uncontrolled erosion. Narrowing the river slightly locally creates a different equilibrium depth in the river. The egg shapes provide safer passage for shipping and better control of bottom erosion.

The Amsterdam-Rhine Canal is 72 kilometres long. It connects the port of Amsterdam with the Ruhr region in Germany and is the busiest canal in the world.