In the period from 1992 to 1993, field surveys were carried out in East Taihu Lake on the distribution, productivity and harvevSt of emerged macrophyte Zizania latifolia. At the same time.the sediment in the distributing zone of the plant was sampled at 15 points, the depth of saft mud was measured and the vsediment samples of differet depth were analyzed on the contents of nitrogen, phosphorous and organic carbon. Experimental study was proceeded to reveal the decaying process of the plant material and its pollution to the water. About 35.47km² of the lake surface of East Taihu Lake was covered by an emerged plant species Zizania latifolia. Its net productivity was 127 600 t/A(fresh weight). Only 9.7% of the product was harvested and 115 204t of the product was left in the lake. It added 1 774g dry plant materiel to every square meter of lake bottom. In the beginning of next summer when the water temperature went up, the remained plant materiel fell into decay and caused serious secondary-pollution to the lake water, forming "Yellow Water". After one year's decaying. large amount of the indecomposable vascular skeleton of Zizania latifolia was left and became the component of the sediment. Intensive harvest of Zizania latifolia may. to a certain extent, resist "Yellow Water", in the lake, but the bevSt measure is to replace it with submerged plant.