Lakes Part 4: Gloeotrichia

By Dylan Moesker


Over the last few weeks in this four part article series, we have been discussing a number of topics that all revolve around lakes. We have talked about phosphorus inputs and algae, trophic status of lakes, tea-stained lakes, and how it all relates to lakes in Muskoka. In this last and final article, I will explain to you what Gloeotrichia is, how it is formed, and what it means for our lakes.


So what is it? Gloeotrichia (glee-oh-trick’-ee-ah)  are small, fuzzy, green floating dots of blue-green algae that have been more frequently noticed in lakes throughout Muskoka, though it does not really act like most of the algae we have discussed.


As a brief recall, we know that phosphorus is the main contributor to plant growth in lakes. Furthermore, we know that excess levels of phosphorus are the main cause of algal blooms for most lakes in Muskoka during late summer, when oxygen levels deplete and phosphorus is released from the sediment. In an oligotrophic lake (like Skeleton Lake), algae is extremely unlikely to bloom due to the high oxygen levels and low phosphorus levels. This is where Gloeotrichia is able to shatter all rules regarding levels of phosphorus and algae. Let me explain.


Gloeotrichia are known to appear in lakes with good water clarity. Essentially, this means that they are more commonly found in very clear lakes that have low-phosphorus levels rather than a lake with high phosphorus levels. How is this possible after I just said that high levels of phosphorus are the main cause of algal blooms?


This blue-green algae is able to acquire phosphorus by a process called “over-wintering”. Basically what happens is it will remain on the lake bottom and slowly grow colonies on the sediment surface where phosphorus is naturally released in lakes. These colonies will absorb any phosphorus being released, even if it is just a small amount. When they are well developed, the algae will release off the sediment and float to the surface, where they will continue to multiply by exposure to sunlight.


During its release and rise to surface waters, this algae will carry phosphorus throughout the water column where it normally wouldn’t be found, creating a possible environment for more algae to develop. This is why it is important for us to reduce the amount of excess phosphorus runoff into our watersheds.


It is still unknown as to why our lakes are hosting these unusual types of algae, though climate change is likely a factor. Luckily, unlike many other types of algae, Gloeotrichia does not produce any toxins and is safe to swim in.


So, what does this all mean for our lakes? New types of algae and organisms found in lakes can be a scary thought. Ecosystems of all kinds are often able to bounce back from a number of stressors, but they are extremely sensitive to foreign or invasive species. We have seen the detrimental effect of the spiny water flea in our lakes and the way purple loosestrife can overrun large areas of natural vegetation. Our water is incredibly important in not only the aesthetics and recreation of Muskoka, but many people get their drinking water from lakes.


As I sum up this final article of this series, I hope everyone understands that we have resource that no one can afford to put in jeopardy, and it is a necessity for us to be conscious of what we put into our lakes. Let’s all work together in keeping the natural beauty of Muskoka as pristine as it can be.



Past articles are available in this blog under the Watershed Notes Articles category or under Past Articles in the Resources section.