From the World Heritage inscription:
The Wouda Pumping Station at Lemmer in the province of Friesland opened in 1920. It is the largest steam-pumping station ever built and is still in operation. It represents the high point of the contribution made by Netherlands engineers and architects in protecting their people and land against the natural forces of water.
The Wouda Pumping Station can be thought of as the next generation of water management after the windmills in the Netherlands. Built in the 1920′s the pump still works and is used when the water levels are high in the spring (normal diesel pumps are now used). The equipment is in pristine condition, including the oil cans used to lubricate the moving parts.