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