IJsselmeer

IJsselmeer
Sentinel-2 photo of the Wadden Sea (top), IJsselmeer (middle), and Markermeer (bottom)
IJsselmeer
IJsselmeer in dark blue
Location	Netherlands
Coordinates	52°49′N5°15′E
Primary inflows	IJssel,Overijsselse Vecht
Primary outflows	Wadden Sea(which empties into theNorth Sea)
Surface area	1,100 km2(420 sq mi)
Average depth	4.5 m (15 ft)
Max. depth	9 m (30 ft)
Surface elevation	−0.4 m (−1.3 ft) (winter) −0.2 m (−0.66 ft) (summer)
Ramsar Wetland
Designated	29 August 2000
Reference no.	1246

Hindeloopen,view of the IJsselmeer

TheIJsselmeer(Dutch:[ɛisəlˈmeːr];West Frisian:Iselmar,Dutch Low Saxon:Iesselmeer), also known asLake IJsselin English,is a closed-off inlandbayin the centralNetherlandsbordering theprovincesofFlevoland,North HollandandFriesland.It covers an area of 1,100 km²(420 sq mi) with an average depth of 4.5 m (15 ft).The riverIJssel,which the lake was named after, flows into the IJsselmeer.

History

Traditional boat on the IJsselmeer

Frozen IJsselmeer, near lighthouseDe Ven

Two thousand years agoPomponius Mela,aRomangeographer, mentioned a complex of lakes at the current location of the IJsselmeer. He called itLacus Flevo.Over the centuries, the lake banks crumbled away due to flooding and wave action and the lake, now called theAlmere,grew considerably. During the 12th and 13th centuries, storm surges andrising sea levelsflooded large areas of land between the lake and the North Sea, turning the lake into a bay of the North Sea, called theZuiderzee.The Zuiderzee continued to be a threat to the Dutch, especially when northwesterly storms funnel North Sea waters towards the English Channel, creating very high tides along the Dutch coast. During the 17th century, Zuiderzee dykes collapsed several times and plans were drawn up to eliminate the threat by draining the bay. Later drainage plans focused on creating fertile farmland, but they never progressed beyond the planning stage. It was only after theflood of 1916that the legislature approved theZuiderzee Works,a major hydraulic engineering project that involved building dykes, draining parts of the Zuiderzee and constructing theAfsluitdijkto keep tides and high water out.

In 1932 theZuiderzeewas closed off by the Afsluitdijk, a 32-kilometre (20 mi) dyke connecting Friesland and North Holland on either side of the Zuiderzee. The Zuiderzee was no longer a sea inlet and was renamed IJsselmeer (Lake IJssel) after theIJsselriver that flows into it, which is also the namesake of the province ofOverijssel.The continuing flow of fresh riverwater soon flushed out the saltwater. Part of the IJsselmeer was later closed off to form theMarkermeer.

From 1929 till 1967, over half the IJsselmeer was drained, creating 1,979 km²(764 sq mi) ofpolders:Wieringermeerpolder,Noordoostpolder,East and SouthFlevoland.

In 1975, a dyke was built betweenEnkhuizenandLelystadas the northern boundary of theMarkerwaard,a planned but never realized polder in the IJsselmeer. This dyke, theHoutribdijkorMarkerwaarddijk,split the IJsselmeer in two parts. The former southern part of the IJsselmeer is now thehydrologicallyseparateMarkermeer.The proposed polderisation of the Markerwaard was abandoned after many of the Dutch population did not want the loss of the traditional seaside (now lakeside) environment and vistas.

In 1986 threepoldersin the IJsselmeer constituted the new province ofFlevoland,the twelfth province of the Netherlands.

The water of the IJsselmeer is now almost completely fresh, the saline having long since been purged. This altered environment has had an impact upon the fish and plantecosystems.The change has been beneficial for Dutch boats, many of which are steel, as the fresh water significantly reduces rusting of the hulls, and there is far less build-up of marine growth (such asalgaeandbarnaclesbelow thebarges' waterlines). This has the knock-on benefit that barges and yachts in the IJsselmeer need far lessantifouling,a coating which is inevitably somewhat toxic to wildlife.

Current use

Due to considerable amounts of water from theRhineflowing through itsdistributaryIJsselinto the IJsselmeer, the closed off bay functions as a largefreshwaterreservoir, serving as a source for agriculture and drinking water. Outlet sluices in the Afsluitdijk regulate the water level of the IJsselmeer.

The IJsselmeer is used for transport and fishing. It also offers a number of opportunities for recreational activity, both on the water and on its shores. Due to the shallowness of the IJsselmeer, the Markermeer and thebordering lakes,its cities and fishing villages remained mostly unspoilt and have many historic buildings.

The IJsselmeer is home to the offshore segments ofWindpark Noordoostpolder.In the future, Windpark Fryslan will also be built in this bay.

See also

• Almere (lake)
• IJsseloog,an artificial island in the Ketelmeer, built as a repository for contaminated silt.
• Ketelmeer,a small bay between the IJsselmeer and the mouth of the river IJssel.
• Lake Flevo
• Markermeer
• Zuiderzee