Water reaches its maximum density at:

1. The density of water does not simply fall as it warms. 2. Water is densest at 4 degrees Celsius, therefore the deepest water in a lake is also the densest. 3. Turnover occurs because water has a maximum density at 4 degrees Celsius. 4. That anomaly is why ice floats and lakes do not freeze solid from the bottom. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 35 'Ecology and the Biosphere', sections 35.1-35.5_