Abstract: According to the site survey for alkaline wastewater from the floatation plants at Dexing Copper Mine,the Dawu River-Le An River was sampled,and the concentration of floatation agenta in the river was dletermined. It is shown that Dawu River was polluted by floatation agents in alkaline wastewater during dry season,At about 1000M down from the join part of Dawu to Le An River,the influence of flotation agents on the pollution is very weaker. The floatation agents in the two rivers are mainly from the accident drainage and water overflow of oretailing dam.