The following is an exerpt from, and used with the permission, of The Associations of Summer Villages of Alberta - Lake Stewardship Reference Guide - 2006 Edition. Please refer to the links page for a full PDF document.
What is a Lake?
lake is a body of standing water entirely surrounded by land, with no
sustained directional flow detectable to the naked eye. Within its
watershed, a lake is often the largest collection point for surface
water from the surrounding drainage area. In general, a lake has
sufficient depth that light does not penetrate all the way to the bottom
in the deepest parts of the lake, and often separates into three
distinct layers of water during the summer.
Alberta’s lakes were
formed 10,000 to 20,000 years ago when the retreating glaciers formed
lake basins by gouging holes in bedrock or loose (glacial) till, or by
leaving buried chunks of ice whose melting shaped and filled lake basins
More recently, humans have created lakes and reservoirs by damming rivers and streams.
A typical lake has distinct zones of biological communities linked to the physical structure of the lake.
The Littoral Zone
The littoral zone is the shallow near-shore area where sunlight penetrates all the
way to the sediment, allowing large aquatic plants (macrophytes) to
grow. This is a highly productive area within a lake. The plants in this
zone provide food and habitat for fish and other organisms, and protect
shores from wave action that may cause erosion.
The Limnetic Zone
The limnetic (or pelagic) zone is the well-mixed surface water layer in offshore
areas, beyond the influence of the shoreline. Within this open water
area you have the photic (or euphotic) zone of the lake, which is the
layer from the surface down to the depth where light levels become too
low for photosynthesis to occur. The profundal (or aphotic) zone is also
located within the open water area of the limnetic zone, and is that
area deep within a lake where light levels are too low for
photosynthesis to occur.
The limnetic zone is a very
productive region of the lake and is dominated by free-floating
microscopic plants and animals (e.g., planktonic algae, cyanobacteria,
phytoplankton and zooplankton) suspended in the water.