The density of water varies with temperature which helps the aquatic animals to live in cold water. At what temperature is the density of water maximum?

Water exhibits a unique property known as anomalous expansion. While most liquids contract and become denser as they cool, water reaches its maximum density at 4°C [t1][t5]. Between 0°C and 4°C, water actually expands as it cools due to the beginning of the formation of a cage-like hydrogen-bonded structure, which increases its volume and decreases its density [t4][t8]. At 4°C, water is at its heaviest and sinks to the bottom of lakes and ponds [t1][t6]. As the surface temperature drops further toward 0°C, the water becomes less dense and remains on top, eventually freezing into ice [t1][t7]. This layer of ice acts as an insulator, while the denser 4°C water remains liquid at the bottom, allowing aquatic animals to survive in sub-freezing external conditions [t1][t6].