Lake Zonation

The following depth zones are recognized in lakes:

a) littoral zone extends from the shore just above the influence of waves and spray to a depth where light is barely sufficient for rooted plants to grow.

b) photic (or "euphotic") zone is the lighted and usually well-mixed portion that extends from the lake surface down to where the light level is 1% of that at the surface.

c) aphotic zone is positioned below the littoral and photic zones to bottom of the lake where light levels are too low for photosynthesis. Respiration occurs at all depths so the aphotic zone is a region of oxygen consumption. This deep, unlit region is also known as the profundal zone.

d) compensation depth is the depth at which rates of photosynthesis and respiration are equal.

e) sublittoral zone, which is the deepest area of plant growth, is a transition between the littoral and profundal zones.

f) pelagic zone (or "limnetic zone") is the surface water layer in offshore areas beyond the influence of the shoreline.

Boundaries between these zones vary daily and seasonally with changing solar intensity and transparency of the water. There is a decrease in water transparency with algal blooms, sediment inflows from rivers or shore erosion, and surface waves.