What is summer stratification? Explain.

Formation of layers of water with different temperatures (Epilimnion, Metalimnion and Hypolimnion) during summer is called summer stratification.
In temperate lakes, three different layers are formed during summer.

• Epilimnion: The warm, oxygen rich, upper layer of water having a temperature range of
  21°–25°C is called epilimnion.
• Thermocline (or) Metalimnion: Below the epilimnion there is a zone in which the temperature decreases at the rate of 1°C per meter in depth, and it is called thermocline.
• Hypolimnion: The bottom layer is the hypolimnion, where water is relatively cool, stagnant, nutrient rich and with low oxygen content (due to absence of photosynthetic activity).