Blue Green Algae


Lake Erie Harmful Algal Bloom Bulletin

To view the most recent Bulletin about the Lake Erie Algae Bloom click on the link below:

General Information

What is it?

Blue-green algae are microscopic, plant-like organisms that occur naturally in ponds, rivers, lakes and streams. Although often blue-green, they can also be olive-green or red.

How to recognize it

Blue-green algae are not normally visible in the water, but populations can rapidly increase to form a large mass or scum called a bloom when conditions are favourable.

Blooms most commonly occur in late summer and early fall. They thrive in areas where the water is shallow, slow moving and warm, but they may be present in deeper, cooler water.

Dense blue-green algae blooms may make the water look bluish-green, or like green pea soup or turquoise paint. Very dense blooms may form solid-looking clumps.

Fresh blooms often smell like newly mown grass, while older blooms may smell like rotting garbage.


One key factor contributing to the growth of blue-green algae is the amount of available nutrients such as phosphorus and nitrogen.

Agricultural, urban and storm water runoff, effluent from sewage treatment plants and industry, and leaching from septic systems can increase the levels of nutrients in water bodies that can promote algae growth.

In Ontario, phosphorus tends to be the nutrient that influences the growth of algae.

If you spot it

Take a cautious approach, as some varieties of this algae can produce toxins that are harmful to both humans and animals.

If you suspect a blue-green algal bloom:

  • assume toxins are present
  • avoid using, drinking, bathing or swimming in the water (call your local health unit for swimming advisories)
  • restrict pet and livestock access to the water

Contact your local health unit for information on health risks associated with blue-green algal blooms.

If it’s near your water supply

Home treatment systems may not remove toxins and can get easily overwhelmed or clogged, so they should not be relied on. Do not boil the water, or manually treat the water with chlorine or other disinfectants, as this could increase the toxin levels.

If you:

  • are connected to a municipal water supply system or other central water treatment and distribution system, you can continue to use the water normally unless notified otherwise by the system operator or the local health unit
  • have your own well supply with a groundwater source (not including shore wells or infiltration galleries), or you receive trucked water in cisterns, you can also continue to use the water normally
  • get your water supply from your own surface water intake in the area of a bloom, you should consider an alternate source of drinking water for the duration of the bloom

Report blue-green algal blooms

If you spot blue-green algal blooms, call the:

Spills Action Centre
416-325-3000 or 1-800-268-6060
TTY: 1-855-889-5775


Take these simple steps to prevent the growth of blue-green algae:

  • use phosphate-free detergents, personal care and household cleaning products
  • avoid using fertilizers on lawns, especially fertilizers that contain phosphorus
  • maintain a natural shoreline on lake and riverfront properties
  • reduce agricultural runoff by planting or maintaining vegetation along waterways and minimizing fertilizer use
  • check septic systems to ensure they do not leak into the water source

Contact your local health unit for more information.

Ontario’s 12-point plan on blue green algal blooms 

Ontario is concerned about the effects of blue green algal blooms in our water. We know there is more to do, and we look forward to working with our many partners.

Ontario has a 12-point plan outlining how we are working with our many partners, to fight algal blooms in the Great Lakes and other lakes and rivers.

  1. Communicate, engage and partner

We will continue to collaborate with other provinces, the federal government, U.S. partners, First Nations and Métis communities, conservation authorities, municipalities and other stakeholders on actions to reduce and address algal blooms. Ontario responds to public questions and reported sightings of algal blooms. Fact sheets and the Guide to Eating Ontario Fish 2015-16 are regularly updated.

  1. Reduce nutrients

Ontario is working to reduce the amount of nutrients that contribute to algal blooms entering water bodies. Examples of projects to reduce nutrients include:

  • Leading a project with municipalities in the Grand River watershed and the Grand River Conservation Authority to reduce nutrients from sewage treatment plants and develop expert peer-to-peer training programs
  • Developing low-impact development technologies and green infrastructure to reduce storm water volume and improve storm water quality
  • Supporting Lake Simcoe Region Conservation Authority’s campaign to promote the use of low-phosphate or phosphate-free products in their watershed
  • Naturalizing shorelines to reduce erosion and improving the ability of coastal and inland wetlands to control water flow and reduce phosphorus loadings
  • Collaborating with greenhouse operators to reduce the release of nutrient-rich wastewater
  • Working binationally, to develop nutrient targets for Lake Erie by 2016
  1. Protect

Local source protection plans use different strategies depending on the risk of algal blooms near drinking water intakes. Plans may manage activities like storage and handling of manure and maintenance of sewage systems, including septic systems, which may contribute nutrients and encourage algal blooms. Other plans encourage more research into the causes of the blooms, increased monitoring and providing information to watershed residents about actions they can take to reduce nutrient run-off

Provincial stewardship funding has supported thousands of voluntary actions such as septic system repairs and upgrades across the province.

  1. Science and innovation

Ontario is a leader in scientific and technical expertise and funds innovative research including:

  • Sponsoring testing optical probes that can determine the presence of cyanobacteria in real-time
  • Assessing new detection, removal and treatment technologies for cyanotoxin at the Walkerton Clean Water Centre
  • Working with partners to better understand the science of algal blooms
  1. Support

Ontario’s Showcasing Water Innovation Fund has contributed $1 million to improve water quality and protect the ecological health of both land and water in the Grand River Watershed. In 2013-14 Ontario’s Great Lakes Strategy contributed more than $2.6 million to address nutrients and harmful algal blooms in the Great Lakes.

The Great Lakes Guardian Community Fund has awarded grants to communities and organizations.  These grants are for projects that help protect water quality and ecological health by naturalizing shorelines, protecting wetlands, clearing beaches and removing invasive species. Grants of $880,701 have supported 42 local projects along Lake Erie alone.

  1. Legislation and regulatory tools

Ontario has legislation and regulations as well as policies and programs in place to protect water quality, including:

  • Environmental Protection Act
  • Ontario Water Resources Act
  • Safe Drinking Water Act
  • Clean Water Act
  • Nutrient Management Act
  • Lake Simcoe Protection Act

Legislation and programs are founded on science and are often ecosystem or watershed based.

  1. Water quality standards and guidelines

The Ontario Drinking Water Quality Standard for microcystin-LR (a common algal toxin) is a maximum acceptable concentration of 1.5 parts per billion or 1.5 micrograms per litre.

  1. Monitor

Ontario has worked with all municipal drinking water systems that take water from the Great Lakes to ensure testing both the intake and treated water for blue-green algae weekly during peak algae season. Working closely with public health units, municipalities and other partners, we provide data to help inform decisions about taking action to protect public health.

  1. Public health

Ontario has a comprehensive protocol in place for responding to harmful algal blooms. This protocol ensures collaboration with local health units and local Medical Officers of Health to effectively manage algal incidents, including quick screening of bloom samples to identify potential toxins.

  1. Contingency plans

Contingency plans are developed by municipal drinking water systems to keep drinking water safe from the potential impacts of blue-green algal blooms.

  1. Analytical laboratory services

If a harmful algal bloom is suspected, samples are submitted to laboratories licensed for analytical testing of total microcystin and microcystin-LR.

  1. Drinking water system courses

The Walkerton Clean Water Centre delivers required refresher courses for drinking water system operators that include responding to and addressing potential algal concerns at drinking water plants.

There is more work to do. We look forward to continue to work with all partners to reduce nutrients and keep drinking water safe.

Updated: September 24, 2014