COVID-19 Wastewater Surveillance in Ontario

Wastewater surveillance is used by public health experts to track and monitor diseases, including COVID-19. This is done by testing community wastewater for the presence of SARS-CoV-2 from infected individuals —called the wastewater signal. This report presents the wastewater signal for Ontario, as well as its sub-regions.

Acknowledgement: The COVID-19 Wastewater Surveillance in Ontario report is based on the original work of the Ontario COVID-19 Science Advisory Table entitled, Wastewater Signals in Ontario, September 6, 2022.

This is a line graph of the estimated COVID-19 wastewater signal for Ontario. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Wastewater signals peaked in April 2023. An increase began in mid-July 2023, leading to a peak in December 2023.

This report is updated Thursdays at 4:30 p.m. ET (based on data extracted on Wednesdays)

For information on source data, citations, definitions, methods and more see our Technical Notes.

Download the data set (Excel format): 
COVID-19 Wastewater Signal Data.

To view an archived version of the report, see Archived Graphs.

This is a line graph of the estimated COVID-19 wastewater signal for the North West region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Small peaks were observed in April 2023 and May 2023. An increase began in mid-July 2023, leading to a larger peak in early November 2023 followed by another large peak at the end of December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the North East region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Wastewater signals had a peak in February 2023. Another small peak occurred in March 2023. An increase began in mid-September 2023 leading to a peak at the end of November 2023 and a smaller peak at the end of December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the Eastern region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Wastewater signals peaked in April 2023. An increase began in mid-July 2023 leading to a peak at the end of November 2023 and another peak at the end of December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the Central East (excluding the GTA) region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Small wastewater signal peaks occurred in February 2023 and April 2023. An increase began in mid-July 2023, leading to a small peak in mid-October 2023. Another increase began in early November 2023, leading to a larger peak at the end of December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the GTA region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. A small wastewater signal peak occurred in April 2023. An increase began in mid-July 2023, leading to a large peak in mid-December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the South West region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Signals fluctuated at an elevated level from February 2023, until they declined in April 2023. An increase began in mid-July 2023, then flattened at the end of September 2023 before increasing again at the end of October 2023 to a peak in mid-November. An increase began in mid-December 2023, leading to a peak at the end of December 2023.

This is a line graph of the estimated COVID-19 wastewater signal for the Central West (excluding the GTA) region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates shown as a dotted line and highlighted with a grey background, covering the most recent three weeks, are more likely to change. Wastewater signals peaked in April 2023. An increase began in mid-July 2023, leading to a small peak in mid-October 2023. Another increase began in early November 2023, leading to a larger peak in early December 2023.

Grey Background: The dotted portion of the curves highlighted with a grey background should be interpreted with caution. These estimates have a higher likelihood of changing in future updates due to a combination of reasons, including but not limited to the analytical approach used, new data submissions for recent days or updates to previously reported data.

Ontario sub-regions: These refer to the following geographical groupings of public health units:

  • North West: Northwestern Health Unit and Thunder Bay District Health Unit.
  • North East: Algoma Public Health; North Bay Parry Sound District Health Unit; Porcupine Health Unit; Public Health Sudbury & Districts; and Timiskaming Health Unit.
  • Eastern: Eastern Ontario Health Unit; Hastings Prince Edward Public Health; Kingston, Frontenac and Lennox & Addington Public Health; Leeds, Grenville & Lanark District Public Health; Ottawa Public Health; and Renfrew County and District Health Unit.
  • Central East, excluding GTA: Haliburton, Kawartha, and Pine Ridge District Health Unit; Peterborough Public Health; and Simcoe Muskoka District Health Unit.
  • Greater Toronto Area (GTA): Durham Region Health Department; Halton Region Public Health; Peel Public Health; Toronto Public Health; and York Region Public Health
  • South West: Chatham-Kent Public Health; Grey Bruce Health Unit; Huron Perth Public Health; Lambton Public Health; Middlesex-London Health Unit; Southwestern Public Health; and Windsor-Essex County Health Unit.
  • Central West, excluding GTA: Brant County Health Unit; Haldimand-Norfolk Health Unit; City of Hamilton Public Health Services; Niagara Region Public Health; Region of Waterloo Public Health and Emergency Services; and Wellington-Dufferin-Guelph Public Health.

How to cite this page: Ontario Agency for Health Protection and Promotion (Public Health Ontario). COVID-19 wastewater surveillance in Ontario. Toronto, ON: King's Printer for Ontario; 2023.

Updated 16 May 2024