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Chemical Characteristics of Lakes

Each lake's chemistry is unique to that lake. The watershed, atmosphere and the lake bottom all affect the chemistry of a lake. Therefore the chemical make-up of a lake is affected by its climate and its basin geology. Humans also have the capability to greatly affect lakes chemistry through the input of nutrients and toxic substances that wash into the lake through stormwater runoff.


Dissolved Organic Carbon

Dissolved organic carbon (DOC) is organic material from plants and animals broken down into such a small size that it is "dissolved" into water.

DOC created by the decomposition of leaves and woody debris that have fallen around or in water are termed humic. This plant material is slowly broken down by organisms into very small particles that are dissolved into water. Yellow to black in color, this humic type of DOC is the most abundant kind found in lakes and streams and can have a great influence on water color.


Dissolved Oxygen

Dissolved oxygen is a major component of lake chemistry as it affects many aspects of a lake's ecology. The amount of dissolved oxygen in the water is an important indicator of overall lake health.

Oxygen is supplied to a lake by:

  • Photosynthesis of aquatic plants, including algae
  • The slow diffusion of atmospheric oxygen

The concentration of dissolved oxygen determines the type of organisms that live in a lake. For example, trout need high concentrations of dissolved oxygen to survive, while other species are more tolerant of low or variable levels of dissolved oxygen.

Mixing of water, aided by wind, distributes oxygen throughout a lake's water column. Cold water can hold more oxygen than warm water. A lake will normally have the capacity to hold more oxygen during the winter than during the summer.



As plankton die and sink to the bottom of the lake nutrients are redistributed. The vertical movement of plankton also affects where nutrients lie.

Nutrients, such as phosphorus and nitrogen, typically increase in the spring from snow melt runoff and spring turnover. During periods with low nutrient concentrations, any additional increase in nutrients into the upper water column may trigger an algae bloom.



Phosphorus is the nutrient that limits plant and algae growth in the lakes in Muskoka. Natural sources of phosphorus include wetlands and precipitation. When larger quantities of phosphorus are introduced to a lake from human sources, algae blooms may result. Human sources of phosphorus include septic systems, fertilizers, agriculture and sewage treatment systems.