Metalimnion - Summer Stratification
This zone lies below the epilimnion and above the hypolimnion and thus forms the intermediate layer which is non-circulating. The metalimnion is characterised by steep and rapid fall in water temperature with increasing depth. Within the metalimnion is present the 'thermocline', the plane at which the temperature drops most rapidly - at least 1 Celsius for each metre of depth.