Summer is Here - and so is Return of Blue-Green Algae

July 24, 2015

With warm weather finally upon us, people across Ontario are enjoying their time outdoors, both on land and in our many lakes and rivers.  Unfortunately – in some parts of the province – this warming of the lakes also contributes to the presence of cyanobacteria – more commonly referred to as blue-green algae. This bacteria forms naturally in lakes, rivers and wetlands under the right environmental conditions, which include warm, shallow water combined with lots of sunlight and nutrients.

Blue-Green AlgaeWhen a large number of these bacteria form, it’s called a bloom. These blooms can release toxins into the water that can pose a health risk to humans and animals during recreational use. Communities affected by the presence of blue-green algae formations may also notice changes to the odour and taste of their drinking water.

The National Oceanic and Atmospheric Administration (NOAA) provides weekly updates and predictions on algae bloom location, size and distribution for western Lake Erie, where blooms are prevalent. The NOAA and their partners recently predicted that the 2015 western Lake Erie harmful algal bloom season will be among the most severe in recent years, close to what we saw in record-setting 2011. But while the blooms are deserving of concern, it’s also important to remember that these blooms are present – and peak – at specific times of the year.

At a July 9 media event and science presentation held at Ohio State University's Stone Lab on Lake Erie, scientists from NOAA noted that much of the Lake Erie will be fine most of the time - the effects of the bloom will vary with winds and will peak in September.

Algae blooms have been a considerable issue for those Ontario communities whose drinking water source comes from areas where the presence of algae blooms has been increasing in past years. OCWA operators who work in communities affected by blue-green algae have seen firsthand some of the impact caused by the presence of the bacteria. OCWA works very closely with Health Units and the Ministry of the Environment and Climate Change to monitor the occurrence of blooms and – working in partnership with our clients – to pro-actively monitor and sample before and during bloom season.

OCWA also supports the Natural Sciences and Engineering Research Council (NSERC) through the University of Waterloo and receives regular updates on various research projects including algae blooms in the Great Lakes of Ontario. 

For more information on blue-green algae, please visit or contact your OCWA Operations Manager.