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{{Short description|Former inland sea in the Netherlands, now the IJsselmeer}}
{{Use dmy dates|date=July 2021}}
{{Redirects here|Zuyderzee|the former French department|Zuyderzée}}
[[Image:Seven_United_Netherlands_Janssonius_1658.jpg|thumb|right|300px|Historical map of the Netherlands (1658) with the ''Zuyder Zee'']]
The '''Zuiderzee''' or '''Zuider Zee''' ({{IPA|nl|ˌzœydərˈzeː|lang|nl-Zuiderzee.ogg}}; old spelling ''Zuyderzee'' or ''Zuyder Zee''), historically called '''Lake Almere''' and '''Lake Flevo''', was a shallow [[bay]] of the [[North Sea]] in the northwest of the [[Netherlands]]. It extended about {{cvt|100|km|mi}} inland and at most {{cvt|50|km|mi}} wide, with an overall depth of about {{cvt|4 to 5|m|ft}} and a coastline of about {{cvt|300|km|mi}}. It covered {{cvt|5000|km2|sqmi}}. Its name is Dutch for "southern sea", indicating that the name originates in [[Friesland]], to the north of the Zuiderzee (cf. North Sea).{{citation needed|date=March 2015}}

It is generally acknowledged that the Zuiderzee existed from roughly 1170, following the devastating [[All Saints' Flood]], until 1932, when the [[Afsluitdijk]] was completed.<ref name="popta">{{cite journal |last1=Van Popta |first1=Yftinus T. |title=No Country for Men: Searching for Late Medieval Submerged Settlements in the North-Eastern Zuiderzee Area in the Netherlands |journal=European Journal of Archaeology |date=2019 |volume=22 |issue=4 |pages=567–587 |url=https://www.cambridge.org/core/services/aop-cambridge-core/content/view/DC359828DE591A9D550B2224D0FDAB35/S1461957119000366a.pdf/no-country-for-men-searching-for-late-medieval-submerged-settlements-in-the-north-eastern-zuiderzee-area-in-the-netherlands.pdf |access-date=17 November 2025}}</ref> The majority of the Zuiderzee was closed off from the [[North Sea]], leaving the mouth of the inlet to become part of the [[Wadden Sea]]. The salt water inlet changed into a fresh water lake now called the [[IJsselmeer]] ([[IJssel]] Lake) after the river that drains into it, and by means of drainage and [[polder]]s, an area of some {{cvt|1500|km2|sqmi}} was reclaimed as land. This land eventually became the province of [[Flevoland]].<ref>{{cite book | title = How it works : science and technology | url =https://archive.org/details/howitworks09mars| url-access =registration| publisher = Marshall Cavendish | location = New York | year = 2003 | page = [https://archive.org/details/howitworks09mars/page/1208 1208] | isbn = 0761473238 }}</ref> Part of the IJsselmeer was also divided into the [[Markermeer]].

==History==

=== Lake Flevo ===
[[File:500vc_ex_leg_copy.jpg|thumb|The region of the [[Netherlands]] {{circa}}&nbsp;500 BC.]]
[[File:50nc_ex_leg_copy.jpg|thumb|The region of the [[Netherlands]] {{circa}}&nbsp;50 AD.]]In classical times the body of water at this location was called Lake Flevo (Flevo Lacus<ref name="EB1911"/>) by [[Roman Empire|Roman]] authors.<ref>{{Cite book |title=Oosthoek encyclopedie |date=17 January 2019 |publisher=OOSTHOEK'S UITGEVERS MIJ. N.V (1916-1925) |language=nl |chapter=Almere |access-date=2024-07-01 |chapter-url=https://www.ensie.nl/oosthoek1916/almere}}</ref> This was the central and largest lake in a region filled with a mixture of lowland and freshwater lakes occupying the area later filled by the Zuiderzee. It was separated from the sea by a belt of [[marsh]] and [[fen]]; at that time, the coastline ran along the line of the [[Frisian Islands]]. A number of streams, including the [[Vecht (Utrecht)|Vecht]], [[Eem]], and [[Yser|Ysel]], fed into the lake. The lake itself fed out into the North Sea through the [[Vlie]] (Latin ''Flevus'').<ref name="EB1911">{{EB1911|wstitle= Zuider Zee |inline=y |volume= 28 | page= 1049}}</ref> It existed in Roman times and the [[early Middle Ages]].

From the Indo-European root ''[[wiktionary:Appendix:Proto-Indo-European/plew-|*plew-]]'' "flow",<ref>{{cite book |last=Koch |first=John T. |url=https://books.google.com/books?id=f899xH_quaMC&pg=PA1195 |title=Celtic culture: a historical encyclopedia |publisher=ABC-CLIO |year=2006 |isbn=978-1-85109-440-0 |volume=1 |page=1195 |quote=Germanic variants, for example, ''Flevo'' (in classical sources) and Modern Dutch ''Vlie(t)'' also occur...}}</ref><ref>{{cite book |last1=de Vries |first1=J. |url=http://www.etymologiebank.nl/trefwoord/vloeien |title=Nederlands Etymologisch Woordenboek |date=1971 |language=nl |quote=*''pleu'', dat nog voortleeft in lat. germ. ''Flevo'', ''Flevum'', mnl. ''Fleo'', ''Fli'', nnl. ''Vlie'' ‘waddenstroom aan de Friese kust’.}}</ref> the name was transmitted by the Roman geographer [[Pomponius Mela]] in describing this region. In his treatise on geography of 44 AD, Pomponius speaks of a ''Flevo Lacus''. He writes: "The northern branch of the Rhine widens as Lake Flevo, and encloses an island of the same name, and then as a normal river flows to the sea". Other sources rather speak of [[Flevum]], which could be related to today's [[Vlie]] (Vliestroom), i.e. the seaway between the Dutch islands of [[Vlieland]] and Terschelling. This last name is grammatically more probable for a geographical indication, which is why it is assumed that Pomponius confused the declension of the word giving the name Flevo. In fact the Vlie formed outfall from the lake into the [[North Sea]].{{Citation needed|date=July 2024}}

In the second half of the twentieth century the [[Flevopolder|Flevopolders]] and a new province, [[Flevoland]], took the name of the body of water which lay there long ago.{{Citation needed|date=July 2024}}

Over time these lakes gradually eroded their soft [[peat]] shores and spread (a process known as [[waterwolf]]). Some part of this area of water was later called the ''Vlie''; it probably flowed into the sea through what is now the [[Vlie]]stroom channel between the islands of [[Vlieland]] and [[Terschelling]].<ref name="EB1911"/>

During a period of rising sea level between 250 and 600 CE, the connection to the sea and the lake were significantly enlarged. A period of lower sea levels followed.
[[File:800nc_ex_leg.jpg|right|thumb|The region of the [[Netherlands]] {{circa}}&nbsp;800 AD. At that time, the lake was called [[Almere (lake)|Almere]].]]

=== Almere ===
Lake Almere is mentioned among others in a life of saints written by Anglo-Saxon Bishop [[Saint Boniface]] in 753, and a deed of gift from the town of [[Urk]].{{citation needed|date=July 2020}} Its etymology may be [[Eel|eels]], in Dutch ''aal'' or ''ael'', so: ''ael mere'' = "eel lake"{{citation needed|date=July 2020}} Presumably, the water of Lake Almere at that time was fresh water or slightly [[brackish]].{{citation needed|date=July 2020}} The name of the new town of [[Almere]] in [[Flevoland]] was given in 1984 in memory of this body of water.{{citation needed|date=July 2024}}

A number of occurrences during the Middle Ages led to the transformation of the lake to an inland sea that would be called the Zuiderzee, which are:
* [[Sea level rise|rising sea levels]] due to global warming known as the [[Medieval Warm Period]].{{citation needed|date=November 2025}}
* excavation of peat by the [[Frisians]] in West Friesland near the [[Vlie]], a river that connected lake Almere to the [[North Sea]].{{citation needed|date=November 2025}}
* floods such as the [[All Saints' Flood (1170)]].

The [[Marsdiep]] between [[Den Helder]] and [[Texel]] was once a river (''fluvium Maresdeop'') which may have been a [[distributary]] of the [[Vlie]]. During the early [[Middle Ages]] this began to change as [[Floods in the Netherlands|rising sea levels and storms]] started to eat away at the coastal areas which consisted mainly of peatlands. In this period the inlet was referred to as the [[Almere (lake)|Almere]], indicating it was still more of a lake, but the mouth and size of the inlet were much widened in the 12th century and especially after a disastrous [[All Saints' Flood (1170)]] and subsequent floods broke through the barrier dunes near [[Texel]] and The land between [[Stavoren]], Texel, and [[Medemblik]] was washed away around 1170.<ref name="buisman360">{{cite book |last1=Buisman |first1=Jan |last2=Engelen |first2=Aryan F. V. van |title=Duizend jaar weer, wind en water in de Lage Landen (Deel 1: Tot 1300) |date=1996 |publisher=Van Wijnen |location=Franeker |pages=360-362 |isbn=90-5194-075-0 |edition=3e druk |language=nl}}</ref><ref name="vos37">{{cite book |last1=Vos |first1=Arent D. |title=Onderwaterarcheologie op de Rede van Texel: waardestellende onderzoeken in de westelijke Waddenzee (Burgzand) |date=2012 |publisher=Rijksdienst voor het Cultureel Erfgoed |location=Amersfoort |isbn=978-9057991943 |pages=37-41 |url=https://www.cultureelerfgoed.nl/site/binaries/site-content/collections/documents/2012/01/01/onderwaterarcheologie-op-de-rede-van-texel/vos_2012_nar_41_onderwaterarcheologie_op_de_rede_van_texel_2.pdf |access-date=16 November 2025 |language=nl |format=Nederlandse Archeologische Rapporten (NAR) 41}}</ref> The disaster marked the rise of [[Amsterdam]] on the southwestern end of the bay, since traders from the [[Hanse|Hanseatic cities]] could now reach the area.<ref name="soest">{{cite web |last1=Van Soest |first1=Arnoud |title='Amsterdam is in de storm geboren' |url=https://onh.nl/verhaal/amsterdam-is-storm-geboren |website=Oneindig Noord-Holland |access-date=15 November 2025 |language=nl |date=9 February 2018}}</ref>

=== Zuiderzee ===
The formation of the Zuiderzee was a gradual process, influenced by several storm surges in 1163/64, 1170, 1173, and especially the Saint Nicholas' Flood ([[:nl:Sint-Nicolaasvloed|nl]]) of 1196, which completed much of what the earlier floods had set in motion.<ref name="buisman360"/><ref name="vos37" /> Human activities – particularly agriculture and peat extraction – are regarded as the primary drivers of the change, as they cause land subsidence through peat oxidation and erosion.<ref name="popta"/> In the 13th century, additional storm surges (1214, 1219, 1220, 1221, 1246, 1248) further shaped the region, which developed into an extensive tidal-flat area with Texel, [[Wieringen]], [[Huisduinen]], and [[Callantsoog]] as islands. Around 1400, the Zuiderzee had reached its full extent, although it was still only two to three meters deep.<ref name="buisman360"/><ref name="vos37" /> In the south and east, the devastation was halted by the high sandy shores of the [[Gooi]], the [[Veluwe]], [[Voorst]], and [[Gaasterland]].<ref name="EB1911"/>

The size of this inland sea remained largely stable from the 15th century onwards due to improvements in [[dike (construction)|dikes]], but when storms pushed North Sea water into the inlet, the Zuiderzee became a volatile cauldron of water, frequently resulting in flooding and the loss of ships. For example, on 18 November 1421, a [[seawall]] at the Zuiderzee dike broke, which flooded 72 villages and killed about 10,000 people. This was the Second [[St. Elizabeth's flood (1421)|St. Elizabeth's flood]].{{Citation needed|date=July 2024}}

The process of creating [[Polder|polders]] had developed to a point by 1667 that the damming of the Zuiderzee was proposed, although a feasible method did not appear until the 20th century.

The Netherlands was part of the [[First French Empire]] between 1810 and 1813. A [[Departments of France|département]] was formed in 1811 and named as [[Zuyderzée]] after the Zuiderzee, whose territory roughly corresponded to the present provinces of [[North Holland]] and [[Utrecht (province)|Utrecht]].{{Citation needed|date=July 2024}}

In 1928, the [[6 Metre|6-meter]] and [[8 Metre (keelboat)|8-meter]] [[Sailing at the 1928 Summer Olympics|sailing events]] for the Amsterdam [[1928 Summer Olympics|Summer Olympics]] were held on the Zuiderzee.<ref>[http://www.la84foundation.org/6oic/OfficialReports/1928/1928.pdf 1928 Summer Olympics official report] {{Webarchive|url=https://web.archive.org/web/20080408184510/http://www.la84foundation.org/6oic/OfficialReports/1928/1928.pdf |date=8 April 2008 }} pp. 271–272, 274.</ref>

=== Zuiderzee Works ===
[[Image:NL-Zuiderzeeworks.svg|thumb|Map of the [[Zuiderzee Works]] in the Netherlands|260x260px]]
{{Main|Zuiderzee Works}}
[[File:Annotated_Zuiderzee_area.png|thumb|Satellite view of the modern region, with parts of the Zuiderzee Works annotated]]
The construction between 1927 and 1932 of a 19-mile long dam (the [[Afsluitdijk]]), under plans originating from [[Cornelis Lely|Cornelius Lely]], enclosed the Zuiderzee. The creation of this dam was hastened by the [[Flood of 1916|Flood of January 1916]]. Plans for closing the Zuiderzee had been made over thirty years earlier but had not yet passed in [[States General of the Netherlands|parliament]].<ref>{{Cite EB1922|title=Zuider Zee|volume=32|pages=1143–1144 |url=https://archive.org/details/in.ernet.dli.2015.83474/page/n1189/mode/2up |last=Lely|first=Cornelius|author-link=Cornelis Lely}}</ref> With the completion of the Afsluitdijk in 1932, the Zuiderzee became the [[IJsselmeer]], and the outer portion of the Zuiderzee became the [[Wadden Sea]]. Large areas of land, mainly for agricultural use, were subsequently reclaimed from the water through the construction of [[Polder|polders]] with dams, pumping, and other hydrological technology. Four had been built by the early 1980s. They were the Wieringermeer Polder built in 1930; the Northeast (Noordoost) Polder, built in 1942; the East (Oostelijk) Flevoland Polder, built in 1957; and the South (Zuidelijk) Flevoland Polder, completed in 1968.<ref name=":2">{{Cite web |title=IJsselmeer Polders |url=https://www.britannica.com/place/IJsselmeer-Polders |access-date=2024-07-16 |website=Encyclopaedia Britannica |language=en}}</ref> A fifth, [[Markerwaard]], began construction in 1963, and became partially complete, but was abandoned in the mid-1980s.<ref name=":2" /> Collectively, this system of dams, dikes, and polders is called the [[Zuiderzee Works]].<ref>{{Cite web |date=2021-09-06 |title=Zuiderzee Works |url=https://earthobservatory.nasa.gov/images/148799/zuiderzee-works |access-date=2024-07-16 |website=NASA Earth Observatory |publisher=NASA |language=en}}</ref>

==Geography==
Around the Zuiderzee many fishing villages grew up and several developed into walled towns with extensive trade connections, in particular [[Kampen (Overijssel)|Kampen]], a town in [[Overijssel]], and later also towns in [[Holland]] such as Amsterdam, [[Hoorn]], and [[Enkhuizen]]. These towns traded at first with ports on the [[Baltic Sea]], in England, and in the [[Hanseatic League]], but later also with the rest of the world when the Netherlands established its [[Dutch Empire|colonial empire]]. When that lucrative trade diminished, most of the towns fell back on fishing and some [[Industrial sector|industry]] until the 20th century when tourism became the major source of income.{{Citation needed|date=July 2024}}

Contained within the Zuiderzee were five small islands,<ref name="EB1911"/> the remains of what were once larger islands, [[peninsula]]s connected to the [[mainland]], or in the case of [[Pampus]], an artificial island.{{Citation needed|date=July 2024}} These were [[Wieringen]], [[Urk]], [[Schokland]], Pampus and [[Marken]].<ref name="EB1911"/> The inhabitants of these islands also subsisted mainly on fishing and related industries and still do in the case of Urk and Wieringen. All of these islands, except for Pampus, are now part of the mainland or connected to it.{{Citation needed|date=July 2024}}

==References==
{{Reflist}}

==External links==
{{Commons category|Zuiderzee}}
*[http://www.zuiderzeemuseum.nl/?language=en Zuiderzee Museum], dedicated to the history and culture of the former Zuiderzee
*[http://www.holland-cycling.com/where-to-go/long-distance-cycle-routes/national-long-distance-cycle-network/zuider-sea-route-zuiderzeeroute Zuiderzee Cycle Route], long-distance cycle route around the former Zuiderzee

{{Coord|52|42|N|05|24|E|region:NL_type:waterbody|display=title}}

{{1928 Summer Olympic venues}}
{{Olympic venues sailing}}
{{Authority control}}

[[Category:Venues of the 1928 Summer Olympics]]
[[Category:Bays of the Netherlands]]
[[Category:Former bays]]
[[Category:Sailing at the 1928 Summer Olympics]]
[[Category:Olympic sailing venues]]