Every lake contains a naturally occurring amount of nutrients - some lakes have more nutrients than others because of their specific features, such as lake depth, area, watershed size, underlying bedrock and climate conditions, among others. To classify the differences between these lakes, scientists established the Trophic State Index which is based on nutrient level and the resulting level of productivity in a lake. There are three main lake types under this classification system: oligotrophic, mesotrophic and eutrophic.
Oligotrophic lakes are usually deep (around 80-100 feet), have low levels of phosphorus and other nutrients, and support little aquatic plant growth. These are cold water lakes that can support Trout and Whitefish due to having high dissolved oxygen content. Lake Trout lakes are of particular importance to The Land Between and Ontario as a whole since only about 1% of lakes (i.e. ~ 2,300 lakes) in the province contain Lake Trout, but this represents a total of 20-25% of all Lake Trout lakes in the world (Ontario Ministry of Natural Resources and Forestry [MNRF], 2015). Lake Trout are great indicators of the health of fragile aquatic ecosystems since they are a sensitive species adapted to a very specific range of environmental conditions. They are also highly sensitive to human disturbance, such as exploitation, nutrient input from cottage septic systems, acidification, invasive species introductions, and habitat destruction. As a result, approximately 5% of Ontario’s Lake Trout populations have already become extinct (MNRF, 2015). Oligotrophic Lake Trout lakes are typically found on the Canadian Shield or northern edge of The Land Between, with underlying bedrock and little soil.
Mesotrophic lakes are in the middle of the spectrum - they are medium in depth (around 60 feet) and have more nutrients than oligotrophic lakes but less than eutrophic lakes. They can therefore support more aquatic plant growth and fish like Walleye and Bass, but occasionally have Lake Trout as well, and can experience natural algal blooms at the surface. Mesotrophic lakes have clear water and many plants growing in the littoral zone.
Eutrophic lakes are naturally the shallowest (around 20 m or less) and contain the most nutrients, especially phosphorus. For this reason, they have abundant vegetation growth, murkier water, and support warm-water fish species like Perch. They may also have more frequent or widespread natural algal blooms.
When nutrients are added to a lake through unnatural sources it can contribute to changes in the lake ecosystem, its water quality, habitats and species, in a process called eutrophication.
To learn what type of lake you live on, try contacting your local MNR field office, or your lake association. We can also provide you with any information that we have on file for your lake if you become a Blue Lakes participant by contacting us at:
The Land Between Charity
Blue Lakes Program Department
Box 1368, Haliburton, ON K0M 1S0
info@thelandbetween.ca
705-457-1222