Water & Sewer

Monitoring Wastewater Overflows and Bypasses

Live map is updated every 15 minutes providing current information for each outfall location. If you remain on this page for an extended period of time you will need to refresh the page to update the map data points.


Map Legend

no overflow  map iconNo overflow within last 48 hours

overflowing map iconSewer currently overflowing

overflow last 48 hours map iconOverflow occurred within last 48 hours

out of service map iconMonitoring temporarily out of service

no live data map iconNo live data available

combined sewer map iconCombined Sewer Area

Community boundary map iconCommunity Boundaries

City boundary map iconCity Boundary

Historical Wastewater Treatment Plant Bypass Log

Updated weekly

Initiation Completion Wastewater Treatment Plant Type of Bypass Duration Volume
May 28, 2021
4:20 pm
May 28, 2021
7:32 pm
Woodward Secondary Bypass 3.20 hrs 18.663 million litres
April 11, 2021
9:03 am
April 11, 2021
12:07 pm
Woodward Secondary Bypass 3.07 hrs 7.092 million litres
March 26, 2021
4:45 am
March 26, 2021
11:46 am
Woodward Secondary Bypass 7.02 hrs 41.994 million litres
February 27, 2021
8:36 am
February 27, 2021
12:52 pm
Woodward Secondary Bypass 4.25 hrs 36.996 million litres
January 2, 2021
1:48 am
January 2, 2021
8:37 pm
Woodward Secondary Bypass

15.13 hrs

50.877 million litres

Table data is not official record.

Historical Combined Sewer Overflow Log

Updated weekly
January 1, 2020 through June 24, 2020 the Overflow Log shows CSO tank overflow events. Starting June 25, 2020 the Overflow Log will show all monitored overflow location events. 

Initiation Completion CSO Outfall Duration Volume
June 14
6:39 pm
June 14
7:03 pm
Wellington CSO Outfall 0.40 hrs  No flow metering present at this location
June 14
9:02 am
June 14
7:11 pm
Wentworth CSO Outfall 1.00 hrs No flow metering present at this location
June 8, 2021
5:32 am
June 8, 2021
5:27 pm
Wellington CSO Outfall 1.34 hrs No flow metering present at this location.
June 8, 2021
5:17 am
June 8, 2021
5:33 pm
Wentworth CSO Outfall 1.77 hrs No flow metering present at this location.
June 3 2021
4:46 am
June 3, 2021
5:20 am
Wentworth CSO Outfall 0.56 hrs No flow metering present at this location.
May 28, 2021
12:01 pm
May 28, 2021
5:01 pm
Wentworth CSO Outfall 5 hrs No flow metering present at this location.
May 26, 2021
7:15 pm
May 26, 2021
7:33 pm
Wellington CSO Outfall 0.29 hrs No flow metering present at this location.
May 26, 2021
7:01 pm
May 26, 2021
7:34 pm
Wentworth CSO Outfall 0.56 hrs No flow metering present at this location.
May 8, 2021
1:43 pm
May 8, 2021
2:07 pm
Wentworth CSO Outfall 0.40 hrs No flow metering present at this location.
April 29, 2021
6:36 pm
April 29, 2021
7:30 pm
Wentworth CSO Outfall 0.82 hrs No flow metering present at this location.
April 18, 2021
3:49 pm
April 18, 2021
4:54 pm
Wentworth CSO Outfall 1.08 hrs No flow metering present at this location.
April 11, 2021
5:51 am
April 11, 2021
10:43 am
Wentworth CSO Outfall 4.27 hrs No flow metering present at this location.
April 11, 2021
7:49 am
April 11,2021 
8:46 am
Wellington CSO Outfall 0.96 hrs No flow metering present at this location.
April 5, 2021
5:28 pm
April 5, 2021
6:12 pm
Wentworth CSO Outfall 0.72 hrs No flow metering present at this location.
March 28, 2021
10:35 am
March 28, 2021
2:08 pm
Wentworth CSO Outfall 3.30 hrs No flow metering present at this location.
March, 26, 2021
10:32 am
March, 26, 2021
9:16 pm

Greenhill CSO Tank

10.73 hrs 33.235 million litres
March, 26, 2021
9:09 am
March, 26, 2021
1:48 pm

Main/King CSO Tank

4.65 hrs

11.934 million litres

March, 26, 2021
7:29 am
March, 26, 2021
10:55 am

Strathearne CSO Outfall

.3.45 hrs No flow metering present at this location.
March, 26, 2021
3:55 an
March, 26, 2021
7:30 am
Wellington CSO Outfall 2.89 hrs No flow metering present at this location.
March, 26, 2021
3:14 am
March, 26, 2021
9:59 am
Wentworth CSO Outfall 6.41 hrs No flow metering present at this location.
March 11, 2021
7:09 pm
March 11, 2021
7:38 pm
Wentworth CSO Outfall 0.48 hrs No flow metering present at this location.
February 28, 2021
12:46 pm
February 28, 2021
1:03 pm
Wentworth CSO Outfall 0.28 hrs No flow metering present at this location.
February 27, 2021
7:34 am
February 27, 2021
9:13 am
Wellington CSO Outfall 0.69 hrs No flow metering present at this location.
February 27, 2021
6:46 am
February 27, 2021
9:46 am
Wentworth CSO Outfall 3.00 hrs No flow metering present at this location
January 2, 2021
1:06 am
January 2, 2021
2:20 am
Wellington CSO Outfall 1.23 hrs No flow metering present at this location
January 2, 2021
12:17 am
January 2, 2021
4:37 am
Wentworth CSO Outfall 3.86 hrs No flow metering present at this location
Table data is not official record.

Historical CSO Overflow and Wastewater Bypass Logs

Why do wastewater bypasses and combined sewer overflow events occur?

The City of Hamilton has a large complex wastewater collection network consisting of both separated sewer and combined sewer systems. Modern areas of the City have separated sewer systems, which consist of sanitary sewers that carry wastewater from toilets and household drains in one sewer system, and storm sewers which carry surface water such as rainwater or snowmelt in another separated system. In older areas of the City a combined sewer system collects both storm water (rainwater or melt water), and wastewater in the same pipe. During periods of heavy rainfall or snowmelt, combined sewers are inundated with large volumes of storm water that can exceed the capacity of the pipes.

Bypasses and CSO events are a necessary operating condition to prevent rainwater and wastewater from backing up and causing basement flooding, surface flooding of our roads and potential damage to the Wastewater Treatment Plants. Flooding from large volumes of storm water at the treatment plants can cause significant damage to mechanical and electrical equipment as well as ‘wash out’ the microscopic organisms needed for secondary wastewater treatment, which can affect the wastewater treatment plant’s ability to function for several days or weeks.

Wastewater Treatment Plant Operations staff monitor incoming flows and system/plant levels and make operational adjustments to the treatment processes as required.

Wastewater Treatment Plant Bypasses
The Wastewater Treatment Plant (WWTP) operations staff can bypass the WWTP at four locations, a total plant bypass, headworks bypass, primary bypass, and secondary bypass.

Plant Bypass
A plant bypass sends untreated sewage from the main pumping station (MPS) wet-well directly to the natural environment. This type of bypass would only be initiated if there was danger of flooding the MPS, or if there was significant maintenance or other works taking place for downstream WWTP processes.

Headworks Bypass
A headworks bypass sends partially treated sewage to the natural environment, bypassing the majority of the WWTP processes.  In the event of a headworks bypass, large solids and heavy grit have been removed from the sewage, and chemicals have been added for phosphorous removal. This type of bypass would be initiated if the maximum primary and secondary bypass capacity was reached and flows continue to increase.

Primary Bypass
A primary bypass sends partially treated sewage to the natural environment, bypassing the majority of the WWTP processes. In the event of a primary bypass, large solids and heavy grit have been removed from the sewage, and chemicals have been added for phosphorous removal. Between May 15th and October 15th each year, primary bypasses will also be disinfected with chlorine, and then the chlorine will be removed. This type of bypass would only be initiated if there was danger of flooding or damage to the primary treatment processes, or if there was significant maintenance or other works taking place for downstream WWTP processes.

Secondary Bypass
A secondary bypass is the most common type of bypass event at a WWTP. A secondary bypass sends partially treated sewage to the natural environment, bypassing the WWTP’s secondary treatment processes (biological treatment and final clarification). In the event of a secondary bypass, large solids and heavy grit have been removed from the sewage, chemicals have been added for phosphorous removal, and the majority of settleable solids and floatable materials have also been removed. Between May 15th and October 15th each year, secondary bypasses will also be disinfected with chlorine, and then the chlorine will be removed. This type of bypass is initiated when WWTP flows exceed the WWTP capacity risking non-compliance of the Environmental Compliance Approval (ECA) for the WWTP and ‘wash-out’ of the WWTP’s biological treatment processes (which would result in partially treated sewage being discharged from the WWTP continuously for days or weeks until the biological processes can be restored), or if there was significant maintenance or other works taking place for downstream WWTP processes.

Combined Sewer Overflow (CSO) Tank Events
Hamilton has nine CSO tanks at eight locations that were built from the 1980’s through 2010 to help add capacity to the combined sewer system The nine large storage tanks hold more than 314,000 cubic metres of diluted wastewater. During rain events the combined sewer overflow tanks will fill and store the excess water. If the storm continues the combined sewer system - now being full and at capacity, will then overflow into the environment.

When the storm stops, and the sewer system and treatment plant have capacity for the volume of wastewater inside the combined sewer overflow tanks, the water is then put back into the sewer system to head to the treatment plant for cleaning.

If the combined sewer system didn’t have the designed overflow option to release wastewater to the harbour, large areas of Hamilton would experience flooding -  which would impact homes, business, roadways, public spaces and public health. Watch a video on how CSO tanks function.

Combined Sewer Overflow (CSO) Outfalls
Hamilton has CSO outfalls from each CSO tank location as well as other unmonitored combined sewer overflow structures within the sewer system that outfall to the environment. These unmonitored structures are primarily passive weir structures that only overflow when the volume within the upstream pipe exceeds the height of the weir wall. These structures provide sewer system relief to minimize flooding impacts to the community when sewer pipes have reached their capacity.     

Sanitary Sewer Overflow Pump Station (SSOPS)
Sanitary sewer overflow pump stations are in limited areas and function when the sanitary sewer system is at capacity and there is risk to flood local homes. These pump stations engage and will send the wastewater to the storm sewer which will then be released into the environment. 

Additional Wastewater Treatment Plant Bypass/CSO Information

Public Health services monitors beaches in accordance with the Ministry of Health and Long-Term Care’s Operational Approaches for Recreational Water Guideline 2018 and the Recreational Water Protocol 2018 under the Ontario Public Health Standards. As outlined in the above protocols, beach samples are collected and tested for E. coli bacteria at least once per week during the swimming season.

Beach sampling results cannot be guaranteed accurate as conditions can change quickly depending on the weather. You should not swim at the beach during and after storms, floods or heavy rainfall. Cloudy water may indicate high levels of bacteria.

For more information on ways to stay safe at the beach, visit the Canadian Red Cross’s website

The Government of Ontario provides fish consumption advisories for Ontario’s lakes and rivers which are available in the Guide to Eating Ontario Fish. You can use this guide and the interactive map to help you identify the types and amounts of fish that are safe to eat from more than 2,400 fishing locations.

Wastewater treatment plant bypass or CSO storage tank overflow events do not have an impact on the quality of the City’s drinking water.

There are 2 Wastewater Treatment Plants in Hamilton:

Woodward Wastewater Treatment Plant
700 Woodward Ave. Hamilton

Dundas Wastewater Treatment Plant
135 King St. E. Dundas

All bypasses are promptly reported to the Ministry of Environment, Conservation and Parks (MECP) Spills Action Centre and to Public Health Services as required by the WWTP’s ECA.

Signage has been added at each outfall location to identify the CSO structure to anyone visiting those areas. The sign includes the name of the individual outfall, a health message, a link to the monitoring webpage and contact information.

CSO Signage

The combined sewer system was installed well before any monitoring technology existed and it was not until the addition of CSO tanks and real time control gates which started in the 1990’s, that locations then had monitoring instrumentation installed. For many of the remaining outfall locations that are unmonitored there are potentially limiting factors to adding instrumentation which include:

  • infrastructure on private property (e.g. active shipping piers),
  • no hydro or communications infrastructure at CSO locations,
  • many of the outfalls are partially or completely submerged underwater where waves and changing water levels impact the function of overflow monitoring instrumentation. 

In 2020, the City will be conducting a study to determine the options available to monitor each location and the costs associated for each. Once the study is complete the details will be presented to the Public Works Committee for consideration.