《水经注·卷九》
羡城北面，水流积聚成潭，方圆十余步，深一丈，东流到内黄，与防水汇合。
羑城北，水积成渊，方十余步，深一丈余。
To the north of Xiancheng, the water accumulates to form a pool, which is more than ten steps in length and width and one zhang in depth. It flows eastward to Neihua and joins the Fangshui River.