Algal Alerts

Algae are simple, typically small aquatic organisms and range in structure from unicellular to multicellular, and as they produce and grow, form colonies that appear on the surface or attached to various substrates. Algae are always present in lakes and rivers and are at the base (primary) of most aquatic food webs, and as such, are critical components of a healthy aquatic environment. Without algae, zooplankton (small animals that feed on algae) would not survive, and this would impact the survival of fish and other animals further up the food chain. Nevertheless, high quantities of algae may affect recreational enjoyment of the water and certain types of algae can be harmful to humans and animals.

Nuisance Algae in Muskoka

As identified in a Muskoka Watershed Council Algae Quick Guide, three main types of algae may potentially bloom in the Muskoka area:

Filamentous Green Algae

These are unicellular or multicellular and may form filaments that range from several millimeters to a meter in length. They can be found free-floating in shallow water on the bottom near shore or attached to submerged objects like rocks. They are typically green in color but can vary in shade depending on age and nutrient content. Some species form colonies that appear as cottony clumps, while others form thready, silky, slippery masses that are slimy to the touch. Blooms usually occur in the spring after heavy runoff or in the summer following hot spells and may appear as clumps or dense mats that float on or just beneath the surface of the water. Blooms can be a nuisance as they may produce a grassy or unpleasant odor. Bloom-forming filamentous green algae commonly found in Muskoka include Spyrogyra, Zygnema, Mougeotia, and Cladophora (shown above).

Chrysophytes

Most are unicellular with a few species forming colonies. They are generally found in low-nutrient lakes and some can move vertically through the water column. Blooms usually occur in spring or early summer. Colonial species may form a bloom below the thermocline in stratified lakes and the water may appear cloudy or coloured. Other species may form a yellowish-green bloom in the upper layers of the lake that is highly visible. Blooms may produce taste-and-odour compounds often described as fishy, musty, or earthy. Bloom-forming chrysophytes commonly found in Muskoka include Uroglena and Synura.

Cyanobacteria (Blue-Green Algae)

These are bacteria that have features in common with algae. Most are unicellular and often blue-green. Cyanobacteria generally fall into two types. First, those that reside and grow in sediments, obtain their phosphorus from the sediment and manufacture their nitrogen through a fixation process. Because these organisms can thrive in low-nutrient waters like those of Kahshe Lake, management through shoreline source reduction may have limited effects.

The other type is planktonic, and these species reside in the water column. They are unique because they can control their buoyancy to move vertically through the water column and position themselves for optimal light, nutrients, and temperature. These types are more responsive to nutrients (primarily phosphorus) in the water and as such, source reductions, particularly of phosphorus, have a greater chance of reducing the potential for blooms to develop.

Some species of both types can produce toxins, making humans and animals sick if exposed to high concentrations. Blooms most commonly occur in late summer and early fall in areas where the water is shallow, slow-moving, and warm; however, they may also be present in deeper, cooler water. Blooms typically look like pea soup or spilled paint with a bluish or greenish color. Fresh blooms often smell like freshly mowed grass, while older blooms may smell like rotting garbage. Bloom-forming cyanobacteria commonly found in Muskoka include Anabaena, Dolichospermum, Aphanizomenon, and Gloeotrichia.

Conditions For Algal Blooms

• Sufficiently high levels of nutrients in either sediments or water (primarily phosphorus and to a lesser extent nitrogen)
• Calm weather conditions and shallow water with low water flow
• Strong sunlight
• High air and surface water temperatures

When conditions are favorable, both benthic and planktonic cyanobacteria as well as other types of algae can increase to levels that result in poor water quality and an algal bloom or scum may form.

Nutrient enrichment, and phosphorus, in particular, have been associated with increases in algal biomass in freshwater systems worldwide. Recent studies indicate that climate change is a potent catalyst for the further expansion of algal blooms because of the warming of surface waters, low wind speed creating slow-moving water, longer periods of open water (fewer ice-covered days), and more intense rainfall which flushes soil-borne nutrients into near-shore waters. Rising air and water temperatures favor bloom-forming planktonic blue-green cyanobacteria because they have higher temperature requirements and because they can regulate their buoyancy under conditions of reduced vertical water column mixing (lake turnover) which occurs under rising surface water temperatures as the season progresses.

Although algal blooms are the primary focus of concern, the sediment-dwelling algae and those that grow on rocks along the shoreline are also of concern. They are aesthetically unpleasant and also make shoreline navigation difficult due to their slimy and slippery nature. As the season progresses, and they complete their life cycle, they can be dislodged from bottom and shore growing locations and can drift into slow-moving water of bays along the shore where they start to decompose.

Many on Kahshe Lake have noticed the unpleasant odors that begin to arise in the late summer and fall as this process takes place. These floating mats also can be mistaken for late-season blooms, as they are dislodged and float into shoreline locations. However, on closer examination, they typically appear less vibrant than the colors of algae in an active bloom.

Algal Bloom Development in Ontario and Muskoka

In a 2011 publication the Environment Ministry’s investigations of algal blooms in Ontario were summarized and their findings confirmed the following trends:

• The total number of algal blooms reported in Ontario increased significantly from 1994 to 2009, and there also were significant increases in the number of blooms dominated by cyanobacteria and chlorophytes.
• Most lakes (50) had a single bloom report, 11 lakes had blooms reported in two years, four lakes had reported in three years, and one lake had reported in eight of the years between 1994 and 2009.
• In 2009, 16 of the 24 blooms reported tested positive for the presence of microcystin, one of several toxic substances that can be released by blue-green algal blooms.
• A significant increase in the day of the year the last bloom was reported in a given year was observed, indicating that blooms are being detected and reported later in the year compared to 15 years ago.

While this Environment Ministry report only covered algal bloom development through 2009, the detection of increasing numbers of harmful blue-green algal blooms has continued to increase, as confirmed by the Simcoe-Muskoka Health Unit in the table below.

Unfortunately, as noted above, harmful blue-green algal blooms (HABs) have now been confirmed in Kahshe Lake in both 2020 and 2021. In 2020, the bloom was located along the northern shoreline in the Oak Road vicinity and was investigated by staff from the Ontario Ministry of Environment, Conservation and Parks (MECP).

In 2021, the first report of a bloom was in the east end of the lake (Kahshe/Shadow River), but this was followed by reports of similar blooms in several areas of the lake, and as such, the alert was issued to cover the entire lake. Further details on these specific blooms and any others going forward have been tabulated at the end of this document and this information will be updated should any further bloom take place in 2023 or beyond.

Why are Algal Blooms of Concern?

Blooms of cyanobacteria are of particular concern in freshwater systems because of the potential of many species to produce toxins. Those produced by cyanobacteria impact human and animal health and can affect freshwater ecosystem processes. They are generally classified into two groups — neurotoxins and hepatotoxins, which can cause acute lethal poisoning; and cytotoxins, which are not highly lethal to animals but show selective bioactivity.

Blooms of cyanobacteria are of particular concern in freshwater systems because of the potential of many species to produce toxins. Those produced by cyanobacteria impact human and animal health and can affect freshwater ecosystem processes. They are generally classified into two groups — neurotoxins and hepatotoxins, which can cause acute lethal poisoning; and cytotoxins, which are not highly lethal to animals but show selective bioactivity.

The severity of symptoms and the level of risk to health depend on how you are exposed to blue-green algal toxins. Human health effects from contact with these toxins may include:

• Itchy, irritated eyes and skin from direct contact through activities such as swimming
• Flu-like symptoms, such as headache, fever, diarrhea, abdominal pain, nausea, and vomiting if large amounts of impacted water are ingested

Health Unit’s Advisory to Property Owners

As a precautionary measure, the health unit urges residents and businesses not to drink water from this lake where blue-green algae are visible and to take the following precautions:

• Do not use the lake water for the preparation of infant formula
• Do not allow pets or livestock to drink or swim in the water where an algae bloom is visible
• Be cautious about eating fish caught in water where blue-green algae blooms occur
• Do not use herbicides, copper sulfate, or other algaecides that may break open algae cells and release toxins into the water
• Avoid water sports activities where an algae bloom is visible

Although not mentioned in the advisory, boiling the water is not recommended as that too will increase the release of the toxins as the cell membranes are ruptured. Some additional facts regarding the health advisory have been confirmed via personal contact with the Muskoka-Simcoe Health Unit:

Are Kahshe and Bass Lakes Susceptible to Harmful Algal Blooms?

The evaluation of algal bloom development by the Ontario Environment Ministry (Winter et al., 2011) included the following observations and conclusions regarding the susceptibility of Ontario lakes to algal bloom development:

• Global increases in HABs have primarily been attributed to nutrient enrichment exacerbated by climate change
• General increases in human activity including cottage and residential development on and around the lakes in which blooms have been reported may have contributed to increases in nutrient inputs, promoting the growth of filamentous green algae and cyanobacteria
• Lakes from which blooms of cyanobacteria were reported were characterized by higher total phosphorus concentrations, (15 µg/L) however, lakes in which blooms were reported varied in total phosphorus concentrations, and 26% of the lakes were classified as oligotrophic, with less than 10 µg/L
• Development of cyanobacterial blooms in low-nutrient lakes indicates that an array of other factors likely contributed to bloom occurrence; these included the type of cyanobacteria involved (benthic vs planktonic) availability of iron which is involved in the release of phosphorus from sediments under low oxygen conditions, as well as environmental stressors including acidification and associated base-cation declines, the presence of invasive species and climate change
• Climate change, specifically rising air temperatures, and low wind conditions promote conditions that favor cyanobacteria and the formation of blooms, including increased water temperatures, more slow-moving waters, more intense precipitation events which can leach nutrients from the shoreline soils, lengthening of the ice-free season, and reduced water column mixing (stratification) as the season progresses

Although it no longer can be discussed in terms of a ‘likelihood,’ it is still important to understand how the total phosphorus levels in Kahshe and Bass Lakes compare with levels in lakes where blue-green algal blooms have been documented. A chart of these findings has been inserted aside and confirms that HABs have developed in several of the impacted lakes that had total phosphorus levels well below those in Kahshe and especially Bass Lakes. Based on these findings, the presence of blue-green algal blooms in November 2020 and October 2021 should not come as a surprise and this development underscores the importance of renewed efforts to drive our nutrient levels even lower than they currently are, as our climate is changing, and creating conditions that favor algal growth and bloom development.

A chart of total phosphorus levels in Kahshe and Bass Lakes over the past four decades (see Water Quality) underscores the fact that in both lakes, levels have remained very steady with no evidence of an increasing or decreasing trend. What this comparison doesn’t tell is how reliable the results from mid-lake, deep water locations like these are at predicting the concentration of nutrients close to shore. A Near-Shore Water Sampling Project to explore the relationship between mid-lake and near-shore levels of algal-friendly nutrients was developed and undertaken in 2021. The findings from that project have been posted under Water Quality and confirmed that near-shore levels of algal-friendly nutrients are not fully represented by mid-lake levels from spring sampling. This was particularly evident as the season progressed, as levels of total phosphorus and some nitrogen compounds were found in near-shore waters in July and September at levels well above those from mid-lake samples following spring sampling.

Summary of Algal Alerts for Kahshe Lake

The table below summarizes the investigative and reporting status of all algal blooms on Kahshe Lake (none were reported for Bass Lake). This table will be updated as any new confirmed HABs are documented and reported.

Preventing Future Algal Blooms

While we can’t do much on a local level to alter the progression of climate change, some actions will reduce the impacts of more intense rainfall events that appear to be flushing soil-borne nutrients from septic systems and from lawns that are grazed by Canadian geese.

• Divert roof drainage and runoff from paths and other hard surfaces away from your septic system and the shoreline. If possible, minimize the areas of hard surfaces on your property and direct rainwater runoff from these areas and from roof gutters into rock-filled drainage pits.
• Keep most of your shoreline as natural as possible with a zone of trees, shrubs, or tall grass between the shore and any lawn area to discourage grazing by Canada geese and to reduce soil and goose poop runoff into the lake. If you have a sandy beach, don’t add any new sand, and do not import sand to create a beach as sand contains lots of algal-friendly nutrients that easily leach or erode into the lake.
• Have a licensed professional pump out and inspect your septic system for failures and deficiencies every 3-5 years and more often for aging systems installed pre-2000. This is even more important if your system smells, shows signs of wet or waterlogged soil, or has excessive vegetation growth on or near the leaching bed.
• Don’t use phosphorus or nitrogen fertilizers or detergents/cleaning agents anywhere near the shore.