Understanding Algae in our Muskoka Lakes

Lake Vernon - Karen ActonHave you noticed there is a lot more talk about algae blooms on our lovely Muskoka Lakes even though the conditions this season have not been conducive to the development of blooms! Over the past 10 years throughout Muskoka there has been an increase in the number of algae blooms reported.

Something I have learned and think you may want to know is that the relationship between algae, algal blooms and water quality is complicated but that the presence of algae in your lake does not necessarily indicate reduced water quality.

What are Algae?

Algae are tiny floating organisms (phytoplankton) or attached (periphyton) plants found in lakes and rivers. They contain chlorophyll and carry out photosynthesis.

Algae are the base component of the aquatic food chain and are a critical component of a healthy aquatic environment. There are many different types of algae found in Muskoka that include diatoms, green algae, pigmented flagellates, and blue-green algae.

Like all life forms algae require a food source and they require sunlight for growth.  It is the amount of nutrients available (especially phosphorus and nitrogen) that will limit the amount of growth of algae in a lake.

There are several other factors that affect the growth of algae in our lakes. Environmental factors that determine the type and number of algae in your lake are:

  • Water temperature;
  • The physical removal of algae as it is flushed downstream;
  • Grazing on the algal populations by microscopic organisms and fish;
  • Parasitism by bacteria and fungi; and
  • Competition from aquatic plants for nutrients and sunlight.

 Phosphorus and Algae

Phosphorus in reasonable amounts is required to help drive aquatic systems. It is a valuable nutrient that promotes plant growth and forms the base of food chains in ponds, streams, lakes and rivers.

Unfortunately, when lakes become nutrient rich it can lead to algae blooms and eutrophication. Algal overgrowth can destroy the appearance of water, make water taste unpleasant and smell, reduce clarity, and change the colour of the lake to a vivid green, brown or yellow.

Natural sources of phosphorus include wetlands and the atmosphere, while man-made sources include:

  • Urban and agricultural runoff
  • Sewage discharges and septic tank seepage
  • Eroded streambanks
  • Fertilizer runoff and detergent wastes.

Nothing can or perhaps even should be done to reduce the nutrients entering your lake from natural sources however reducing the nutrients from man-made sources should be minimized and can hopefully prevent excessive algae growth in the future.

What are Algal Blooms

When there is excessive growth of one or more species of algae, it is called a “bloom”.  Algal blooms can happen at any time of the year but are most common in summer.  Algal blooms usually occur after calm, hot weather when the water gets warm. Blooms are caused by several factors but an increase in nutrients and the right weather conditions often result in the formation of a bloom; just as fertilizing a lawn makes the grass grow faster. In other instances, something may change in the environment to favour one species of algae over another, leading to a population explosion.

One of the most serious consequences of an algae bloom occurs when the bloom dies off. As algae die, they sink to the bottom of the lake and decompose, depleting oxygen levels. The depletion of oxygen in the bottom layer of the lake can free phosphorus trapped in the sediments and reduce the amount of oxygen available for the survival of other aquatic organisms, including fish.

Algal Blooms can occur sporadically in lakes that don’t have elevated levels of nutrients. Therefore, increased levels of phosphorus cannot be relied on as the sole rationale for sporadic or individual algal blooms, and the presence of an algae bloom does NOT necessarily indicate nutrient enrichment.

Blue-green Algae

Blue-green algae, or cyanobacteria, are photosynthesizing bacteria, not plants. Blue-green algae are commonly found in lakes and ponds. Some types of blue-green algae produce toxins while others do not.

The only way to determine if a sample of blue-green algae contains species capable of producing toxins is to analyze the sample in the lab.

Blue-green algae blooms are likely to occur during sunny, calm weather when high concentrations of nutrients are present in water. Fresh blooms may smell like fresh-cut grass, while older blooms may smell like garbage. When the algae die and decompose, toxins may be released in those species that produce them. Symptoms from drinking water contaminated with blue-green algae include headaches, fever, dizziness, diarrhea, abdominal pain or stomach cramps, sore throat, nausea and/or vomiting.

Blue-green algae have several characteristics that enable them to out-compete other species of algae, including:

  • The ability to adjust their buoyancy so they can float or sink depending on light conditions and nutrient supply
  • Using nitrogen fixation to maintain high rates of growth when other forms of nitrogen are depleted
  • They are less favoured by predators than green algae because they produce chemicals that make them ‘taste bad’.

 

So here is the bottom line as a cottage owner or renter. Algae are a normal part of the ecology of aquatic life. They usually pose no risk to us. They need specific conditions to “bloom” some of which we can help mitigate by being aware of our phosphate loading from our septic system. This can be done by selecting our detergents and fertilizers with care.  Most algae are not harmful to humans but blue-green algae can cause sickness and in extreme cases serious illness. Water that has a blue-green bloom should be avoided.

I AM NOT AN EXPERT ON ALGAE but I do feel that good stewardship of our lakes is vital and the Muskoka Watershed Council and Muskoka Water Web have great resources to assist us in doing that.

Algal bloom sightings can be reported to the Ontario Ministry of the Environment and Climate Changes Spills Action Centre at 1-800-268-6060.

Advertisements