In many lakes in summer that is a warm low - density layer ( epilimnion ) lying above a colder denser layer ( the hypolimnion ) , the zone of rapid temperature change between the two layers being celled the thermocline 夏季，多数湖中温暖的低密度水层（湖面温水层）在寒冷的较高密度水层（湖底净水层）之上，中间夹有温度改变较快的水层（变温层） 。
