IJsselmeer

The IJsselmeer is a large, closed-off freshwater lake located in the central Netherlands. It borders the provinces of Flevoland, North Holland, and Friesland.

The lake is named after the IJssel river, which flows directly into it. This river provides approximately 70% of the lake's water. The remaining water comes from local rainfall, streams, and various pumping stations. Today, the IJsselmeer serves as a massive freshwater reservoir for the country. It is vital for managing water levels and providing resources for people.

The history of this area began thousands of years ago. A Roman geographer named Pomponius Mela mentioned a group of lakes here called Lacus Flevo. Over many centuries, the banks of these lakes crumbled due to waves and flooding. This caused the water body, then known as the Almere, to grow larger. By the 12th and 13th centuries, rising sea levels and storm surges flooded the land. This turned the area into a large bay of the North Sea known as the Zuiderzee.

The Zuiderzee presented a constant danger to the Dutch people. Northwesterly storms would often funnel North Sea water toward the English Channel. This caused very high tides along the Dutch coast. During the 17th century, several dykes in the Zuiderzee collapsed. While early plans existed to drain the bay for farmland, they did not move forward for a long time. It was only after a major flood in 1916 that the government approved the Zuiderzee Works. This was a massive hydraulic engineering project designed to protect the land.

The Zuiderzee Works changed the geography of the Netherlands forever. Construction began in 1927 to build dykes and drain parts of the bay. In 1932, workers completed the Afsluitdijk, a massive dyke connecting Friesland and North Holland. This structure closed off the Zuiderzee from the sea. Once the tides were blocked, the river water from the IJssel flushed out the salt. The salty bay became the freshwater IJsselmeer.

Between 1929 and 1967, engineers drained over half of the IJsselmeer to create new land. These areas are called polders. Specific polders created include the Wieringermeerpolder, the Noordoostpolder, and East and South Flevoland. In 1986, these three polders were organized into the new province of Flevoland.

Another project involved the Houtribdijk, a dyke built between Enkhuizen and Lelystad. This dyke split the lake into two sections. The southern part is now a separate body of water called the Markermeer. Some plans to drain even more land, called the Markerwaard, were abandoned because people wanted to keep the lakeside views.

The shift to freshwater has had many practical effects. For Dutch boat owners, the lack of salt is a major benefit. Saltwater causes steel hulls to rust, but freshwater significantly reduces this problem. It also prevents marine growth like algae and barnacles from attaching to boats. This means yachts and barges need less antifouling, which is a coating that can be toxic to wildlife. The lake also functions as a reservoir for drinking water and irrigation for agriculture.

Managing the water level is a constant task for the government. Outlet sluices in the Afsluitdijk regulate the lake by moving excess water into the Wadden Sea. However, tides and strong winds can sometimes make this difficult. Because rising sea levels are a growing concern, the government is installing more pumps. The IJsselmeer is also used for fishing, transport, and recreation. In the summer, water is used for irrigation and to flush salt from reclaimed lands. In the winter, the process reverses to manage rainwater.