Originally published in Lake of the Woods Area News, Volume 54, Number 5, Winter 2024
As we try to understand how the health of lakes has been changing, it’s important to revisit the basic question: What even is a lake?
On the surface (pun intended), this may seem like a simple question. But definitions of lakes change depending on the context within which we discuss them.
You can, however, identify some general characteristics of lakes in order to differentiate them from other water features and understand what a lake is in the context of your life.
Defining a lake involves considering its physical, chemical, biological, and social features.
What do I picture when I imagine a lake? Physical limnology:
Lakes form when water collects in large indentations of the earth’s surface called lake basins. Basins form in different ways, like in imprints left by moving glaciers, trenches formed from moving tectonic plates, areas upstream of dams, and abandoned parts of rivers.
Size and surface area help most people identify lakes by sight. Most people recognize lakes as large waterbodies.
Defining a lake becomes more complex when you also consider the waterbody’s depth and bottom structure (i.e., bathymetry). A waterbody may have a large surface area, but if it’s shallow, is it really a lake?
According to some limnologists, lakes range from shallow (sometimes less than 1 metre deep) to very deep. With this in mind, it is important to note that since lakes can range in depth, the dynamics of specific lakes will be influenced by their depth.
When asking questions about the health of lakes and understanding ongoing lake research, context is always important to consider. Being aware of the context in which a lake is being discussed will help you identify how it’s being defined and what kind of lake it may be.
Probably the most consistent strategy for defining a lake involves water movement. This is easiest to understand when comparing a lake to a river. Lakes are lentic habitats (i.e., habitats with slow-moving water) while rivers are lotic (i.e., habitats with flowing water).
Try looking at a waterbody on a windless day—is the water still moving or is it calm? To the human eye, lakes will remain calm on a windless day, while a river or stream will continue to flow.
Why is the water that colour? Chemical limnology:
Lakes are not necessarily differentiated from other waterbodies solely based on chemistry. However, the proportions and movement of chemicals in a waterbody can help us describe how it fits into the landscape.
Lake chemistry relates to physical features, such as the lentic nature of lakes, lake basin geology, and how water flows through the lake. Closed lakes, for example, lose water via evaporation (compared to open lakes that have stream or river outlets). Closed lakes are usually saltier than open ones because evaporation leaves behind dissolved chemicals and nutrients.
Have you heard of the Dead Sea? This well-known lake is so salty that only highly specialized organisms can live in or near it and visiting swimmers can float on their backs and read without getting their book wet.
Are there fish in it? Biological limnology:
Lakes and other waterbodies are important and complex ecosystems. The biota living in a waterbody can hint at whether it’s a lake or not. As lakes are considered big bodies of water, it’s helpful to consider what and how larger species use the water.
Lakes are often permanent habitats for fish because they can be big enough to retain good habitat throughout the year—sometimes even in -40°C temperatures.
Not all lakes, however, support the same animal communities, so there is no rule for what lives in lakes versus other waterbodies.
What does this waterbody mean to us? Situated limnological knowledge:
Human cultures around the world recognize lakes as essential parts of their environments. Living in the lake-rich Canadian boreal ecozone, it’s clear that people depend on lakes for navigation, recreation, education, survival, and wellness.
Lakes can be identified by their unique social and mystical relevance. For some Indigenous peoples, lakes have Mishibeshu, or Water Panthers, that influence the weather, safety, and sometimes prosperity of lakes for humans. Mishibeshu may shape each lake in a different way, which controls the unique characteristics of that lake.
In short, when differentiating a lake from other waterbodies, the things to remember are:
- Lakes are inland basins full of water
- Lakes are large in surface area
- Lakes have slow-moving water
- Lakes are complex ecosystems
- Lakes differ across cultures and geographies—there is no one single way to define a lake.
To learn more about freshwater health and the incredible science that takes place at the world’s freshwater laboratory, visit iisd.org/ela.
