Traditional boat on the IJsselmeerFrozen IJsselmeer, near lighthouseDe Ven
Two thousand years agoPomponius Mela, aRoman geographer, 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 levels flooded 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 1916 that the legislature approved theZuiderzee Works, a major hydraulic engineering project that involved building dykes, draining parts of the Zuiderzee, and constructing theAfsluitdijk to keep tides and high water out.
Construction began in 1927 and in 1932 theZuiderzee was 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 theIJssel river that flows into it, which is also the namesake of the province ofOverijssel. The continuing flow of fresh river water soon flushed out the salt water. Part of the IJsselmeer was later closed off to form theMarkermeer.[4][5]
In 1975, a dyke was built betweenEnkhuizen andLelystad as the northern boundary of theMarkerwaard, a planned but never realized polder in the IJsselmeer. This dyke, theHoutribdijk orMarkerwaarddijk, split the IJsselmeer into two parts. The former southern part of the IJsselmeer is now thehydrologically separateMarkermeer.[7] 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 threepolders in 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.[8] This altered environment has had an impact on the fish and plantecosystems.[9][10] The change has been beneficial for Dutch boats, many of which are steel, as the freshwater significantly reduces rusting of the hulls, and there is far less build-up of marine growth (such asalgae andbarnacles below 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.
Due to considerable amounts of water from theRhine flowing through itsdistributaryIJssel into the IJsselmeer, the closed-off bay functions as a largefreshwater reservoir, serving as a source for agriculture and drinking water. Outlet sluices in the Afsluitdijk regulate the water level of the IJsselmeer by putting the excess into theWadden Sea through control locks. Excess water is also drained from the Markermeer in this same manner. However, this isn't always possible due to differing water levels, tides, and strong winds. Rising sea levels are also a growing problem. For this reason additional pumps are being added.[11] Without many of these features, the national capability for flood risk management and water management would be hindered. The rising sea levels are of growing concern to the government, who is expanding pump installation at a growing rate.[12]
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.[13]
In the summer the excess water is further diverted and used to provide more drinking water, irrigation, water recreations, and to flush excess salt in the reclaimed lands. In the winter, this is reversed to accommodate additional rainwater.[11]
The IJsselmeer is primarily fed by the River IJssel (70%), this amount can vary by snowfall and rainwater. The rest comes from local rainwater and water from other sources such as streams and pumping stations.[11]
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