Aquatic life is the richest and most abundant in the shallow water where sunlight can reach the bottom. This is the littoral zone found about the edges of lakes. The plants and animals found here vary with water depth and a distinct zonation of life exists from deeper water to shore.
Submerged plants, such as the algae chara and the pond weeds or potomogetons are found at water depths beyond that tolerated by submerged vegetation. They serve as supports for small algae and as cover for swarms of minute aquatic animals.
Starting in deep water, the submerged plants are highly modified in structure. The buoyance and protection of water eliminates the need for supporting tissues in the stems.
Air chambers and passages are common in leaves and in the cortex of stems. Oxygen that is produced by photosynthesis is stored for use in respiration. Since the leaves lack cuticle, submerged plants can absorb nutrients and gasses directly from the water through thin and finely dissected or ribbon like leaves. The roots are usually small and poorly branched and lack root hairs. For the most part, vegetative reproduction of these plants is highly developed.
As sedimentation and accumulation of organic matter increases towards the shore and the depth of the water decreases, floating rooted aquatics such as pond lilies and smart weeds begin to appear.
Many of these floating plants have poorly developed root systems but highly developed aerating systems. Supporting tissue is greatly reduced and the spongy tissue in the stems and leaves is filled with large air spaces. The upper surfaces of floating leaves are heavily waxed to prevent the clogging of stomata by water. Underwater leaves of these same floating plants are like those of small submerged plants, very thin and small, while the floating leaves are usually large and different in form. The leaves and stems are leathery and tough and able to withstand the action of the waves.
Floating plants offer food and support for numerous herbivorous animals that feed both on phytoplankton and the floating plants. The undersides and stems of plants support a highly varied assemblage of organisms among them protozoans, hydras, snails and sponges.
In the shallow water, beyond the zone of floating plants grow the emergent plants whose roots and lower stems are immersed in the water and whose upper stems and leaves stand above the water. Some of these emergent plants with narrow, tubular or linear leaves such as bull rushes, reeds and cattails. With these are associated such broad leaf emergent plants as pickerel weed and arrowhead.
The distribution and variety of plants vary with the water depth and fluctuation of water level. Fish such as pickerel and sunfish find shelter, food and protection among the emergent and floating plants.