XuanwuLakewasconnectedwiththeYangtzeRiverinancienttimes.IntheSixDynasties,alongdikewasbuiltonthenorthsideofthelake.Duetothecontinuousimpactoftheriver,itwasisolatedfromtheYangtzeRiverandformedanindependentlake.Onthisday,XuanwuLakestilldependsonthewaterfromtheYangtzeRiver.
XuanwuLakeisatectoniclakeformedbyYanshanorogeny.ItwasnamedSangpoLakeinancienttimes.Later,itwascalled"Houhu"becauseitwaslocatedintheshadeofZhongshanMountain.AfterthecapitaloftheeasternWuDynastywasmovedtoJiankang,therewasapalaceonthesideofHouhu,andthewaterfromHouhuwaspouredintothepalace.BecausethelakewasinthenorthofTaicheng,itwascalled"Beihu".Inhistory,itissaidthatinthelastyearsofWuDynasty,themotherofXuansai,anofficialofDanyangCounty,wasswimminginHouhulakeattheageof80.Shesuddenlyturnedintoaturtleanddiedforathousandyears.Therefore,peoplealsocallHouhuLake"Lianhu".
AsforthenameofXuanwuLake,itwasfirstseenin448.Itissaidthatblackdragonappearedinthelake,soitwasrenamed"XuanwuLake".Ofcourse,itisimpossibletohaveadragoninthelake,butsomepeoplespeculatethatthetwoso-calledblackdragonsmaybecrocodilesintheYangtzeRiver,becauseXuanwuLakewasstillconnectedwiththeYangtzeRiveratthattime,crocodilescouldtakeadvantageofthetidetovisitthelake.Beforethethunderstorminsummer,becauseofthehotweather,theycameoutofthewaterandweremistakenasblackdragons.