More aquatic life is present in the littoral zone around the lake edges where sunlight penetrates to the bottom and supports rooted aquatic plants. The shallow waters are sometime covered with duckweeds and a variety of animals such as insect larvae, rotifers, crustaceans, hydras, snails, and flatworms. Closer to the shore are plants such as pond lilies, bullrushes, and cattails. Dragonflies and damselflies lay their eggs on stems of these plants just below the water line, and the surrounding waters teem at certain seasons with tadpoles, fish fry, leeches, and insects such as diving beetle and water boatmen. Pickerel, sunfish, and other fish find plenty of food and shelter among the plants.
Temperature has a great influence on the seasonal activities in a lake.
As a result, water at 4C sinks beneath water that is warmer or colder. In winter water cooled below 4C rises above water at 4C and at 0C the surface water freezes. In spring, the ice melts and the sun warms the surface waters, which sink as they approach 4C, forcing colder water below to rise to the surface. This spring overturn is important because it brings nutrients from the bottom to the surface and carries oxygen down to deeper waters. In the summer you may have been swimming in a lake where the surface layer is warm, but at your toes you feel much colder water.