How Old is your Lake?
How old is your lake?
Bodies of water, like all living things, go through an aging process. In lakes, it’s called “Eutrophication.” Lakes age at different rates, some taking only a few hundred years, others taking thousands of years to grow old.
As a rule, the more nutrients they get, the faster lakes age. In general (and there are many exceptions) a young lake was most recently covered by a glacier. Older lakes were uncovered earlier, as glaciers receded from south to north.
But, your “old” lake may only be a few hundred years, or even just a few decades old. Or you could be on a young lake that’s many thousands of years old. It’s not years that define the age of your lake — it’s their “traits.”
Young lakes are called “Oligotrophic.”
Example: Lake Superior
Traits of young lakes —
Steep shorelines at the water’s edge
Primarily conifers (pines) along the shore
Deep with steep drop offs near shore
Lake bottom is mostly rocky
Water is extremely clear
Has very few, if any, aquatic weeds
High oxygen concentrations
Populated with cold water fish — trout, steelhead, salmon
Over time, shorelines erode and become less steep. Rocks on the lake bottom grind against each other creating sand.
More plant life emerges on shore and in the water. The lake reaches middle age.
Middle-aged lakes are called “Mesotrophic”
Example: Lake Michigan
Traits include:
Gentler, sandy shorelines
Pines and deciduous trees, like oak, maple and ash along the shore
Mostly sand lake bottom
A few aquatic weeds and more diverse plants on the shoreline
Less deep than oligotrophic lakes
Water is still quite clear
Good oxygen content
Supports cold and warm water fish, like bass, perch and bluegill
Over more time, lakes gain nutrients as leaves, plants, and other organic material decays. The lake bottom fills with silt and sediment. The lake has become an old lake.
Old lakes are called “Eutrophic”
Example: Your Lake (or you probably wouldn’t be reading this).
Traits include:
Gentle, mostly flat shorelines
Mostly deciduous trees along the shore, many types of plants on shore
Quite shallow compared with younger lakes
Less oxygen in water
Water is usually “stained” from organic material
Heavy aquatic weed growth
Few cold water fish. But bass, panfish, pike and carp thrive
It is the nature of lakes to fill in. As time passes, your lake becomes shallower, more shoreline erodes, trees fall in, leaves, dust and dirt blow in, weeds become thicker and grow out farther, die, decay and add to the bottom.
There are several names for bodies of water that were once lakes. They’re called bogs, swamps, wetlands and finally, “darn good farmland!” It’s a slow, but inevitable, natural process.
In the distant future, new glacial eras will likely create new landscapes and carve out new lakes. The aging process will begin again.
— Doug Fast
