Thirty million years ago, the collision between the Philippine and Eurasian Plates caused the Chihshang Fault to thrust to the northwest, forming a fault depression. Subsequently, overflow from the Hsinwulu River and accumulations of spring water resulted in the formation of a lake located 269 meters above sea level, as well as Taiwan's only inland marsh.
三千萬年前，菲律賓板塊與歐亞大陸板塊的世紀擠壓，致使池上斷層向西北逆衝，形成一個斷層窪地，之後新武呂溪伏流、湧泉匯集，形成一個海拔高度達 269 公尺的斷層湖泊，也是台灣唯一的內陸池沼。