When Algae Go Bad

By Dr. Norman Yan


In a previous article I argued that “we’d be stupid, hungry, and dead without algae” in the waters of the world, because every other breath we take and some essential biochemicals in our bodies are directly produced by aquatic algae.


Thus, for the vast majority of the time, and in the vast majority of our lakes, algae are good for both us and for Muskoka’s aquatic ecosytems. However, on rare occasions, algae can “go bad”, and form what are called Harmful Algal Blooms, or HABs.


Most HABs occur in estuaries or along developed coastlines in the oceans. These HABs are called red tides, and are formed of very dense accumulations of a single-celled algae, called a dinoflagellate. During red tides these algae are so numerous they stain the ocean red with their pigments, and red tides are dangerous, releasing toxins that can harm fish, shellfish, marine mammals, birds, and people. They can even harm regional maritime economies when fisheries have to be closed.


Red tides are restricted to salt water environments, but there are also two main types of HABs that can occur in freshwaters. The first kind is a blue-green algae bloom. Blue-green algae are actually a kind of bacteria, called Cyanobacteria and blue-green blooms are fairly common in hot summers in phosphorus-rich lakes. This is one of the reasons why so much attention is given to phosphorus management in and around our lakes in Muskoka. When they occur, blue-green blooms may form unsightly surface scums or sub-surface accumulations of algae, and when the masses sink they consume bottom-water oxygen which is so essential to deep water life, including trout.


Some blue-green blooms can also release toxins, especially a large family of chemicals called microcystins. At high densities, microcystins can irritate the skin and eyes of swimmers. They are also toxic if ingested in large amounts, and livestock have been killed when animals have drunk from bloom-infested waters. Thus, blue-green blooms are serious business, leading, when microcystins are present above action thresholds, to orders from health authorities to not draw water from or swim in affected lakes.


We don’t know all the details of what causes these blooms, but we do know that warmer growing seasons and elevated phosphorus levels promote blooms. The good news is that blue-green blooms are very rare in Muskoka lakes, with the Ministry of the Environment and Climate Change (MOECC) reporting only one such incident in 2012. We also will soon know more about these types of blooms, because this is an active area of research by the Canadian Water Network’s Muskoka watershed research node.


The second type of HAB is formed by a few species of the “golden-yellow algae” called Chrysophytes, and when they bloom they turn the water golden-brown in large patches. These blooms are usually quite short-lived, but they may pose taste and odour problems when they do occur. I happened to be on Harp Lake, east of Huntsville, one summer when such a bloom occurred. It formed an obvious, large, brownish patch in the middle of the lake, but lasted only a few weeks, forming more of a curiosity than a nuisance, in that case. These blooms can occur in soft-water, slightly acidic, nutrient-poor lakes, and we have lots of those sorts of lakes in Muskoka, but the good news is that they are quite rare. The MOECC recorded only two chrysophyte blooms in Muskoka lakes in 2012.


The vast majority of Muskoka lakes are in good condition, as far as algae are considered. There are enough algae to support the diverse food chains supporting the fish, amphibians, turtles and birds that we so value, but not too many algae to reduce water clarity and form harmful blooms. Let’s manage our watershed wisely to keep it this way.



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