| reference = <ref name="smhi">{{citeCite web |year=2001 |title=Vattenståndsmätningar i Hjälmaren |url=http://www.smhi.se/sgn0102/n0205/artikelserier/v200111_18.pdf|title|url-status=Vattenståndsmätningardead i Hjälmaren|publisher=[[Swedish Meteorological and Hydrological Institute]]|year=2001|accessdate=2009-01-03|url-status=dead|archiveurl=https://web.archive.org/web/20070929091823/http://www.smhi.se/sgn0102/n0205/artikelserier/v200111_18.pdf| |archivedate=2007-09-29}}</ref>
}}
'''Hjälmaren''' ({{IPA-sv|ˈjɛ̂lːmarɛn}} <small>or</small> {{IPA-sv|ˈjɛ̂lːmaɳ|}}<ref name="Bergman">{{citeCite book |last=Jöran Sahlgren |url=http://runeberg.org/ortnamn/0016.html|author1=JöranSahlgren|author2=Gösta Bergman|title=Svenska ortnamn med uttalsuppgifter |languagelast2=svGösta Bergman |year=1979 |page=12 |language=sv}}</ref>), also spelled '''Jälmaren''',<ref name="Bergman" /> is [[Sweden]]'s fourth largest lake. It is situated in the [[Central Swedish lowland]] and drains through [[Eskilstunaån]] into the adjacent Lake [[Mälaren]], which in turn drains into the [[Baltic Sea]], west of [[Stockholm]]. It is connected by waterway with Stockholm by the 13 kilometres long [[Hjälmare kanal]].
It is bounded by the [[Provinces of Sweden|provinces]] of [[Södermanland]], [[Närke]], and [[Västmanland]].
Hjälmaren is 63 kilometres long, about 20 kilometres wide, and has an average depth of 6 metres, and a surface of 483 km². The town of [[Örebro]] is situated at the western end of the lake.
The lake itself is an iconic part of Sweden with music festivals taking place on the banks of the lake.{{Citation needed|date=January 2017}} NotableSeveral bandsnotable tobands playplayed there, areincluding [[The Smashing Pumpkins]], [[Sonic Youth]] and [[Pearl Jam]].
Between 1878 untiland 1887, thea projectdamming [[Hjälmarsänkningen]]project lowered the surface level of Hjälmaren {{Convert|1.3m3|m|ft}} to free up land for agriculture and to reduce the risk of flooding.
The rebel [[Engelbrekt Engelbrektsson]], was assassinated in 1436 at [[Engelbrektsholmen]], an islet in Lake Hjälmaren.