Combined sewer overflows
During heavy rain or snowmelt, older combined sewer pipes — which carry both sewage and stormwater in the same pipe — can become overwhelmed. When the volume of water exceeds what these pipes can handle, sewage can back up into basements or overflow into the environment.
Older systems were built with overflow points that act as a pressure release, letting excess water escape before it backs up into homes. This protects basements from flooding, but it also means under-treated sewage can be released into ditches, rivers and lakes, raising health and environmental concerns.
Niagara Region no longer installs combined sewers and is investing in infrastructure upgrades to reduce and eventually eliminate overflows.
Overflow monitoring and reporting
Overflow map
Real-time status
Get near real-time statuses for Niagara Region–owned overflow sites. Sensor readings are subject to final validation.
Overflow data
Quarterly reporting
Overflow records are updated four times a year. Get recent overflow events and historical summaries by city or town.
Overflow warnings and water safety
Signs are posted at publicly accessible sites near overflow locations, warning of potential hazards after heavy rain or snowmelt. Because overflows can affect recreational water quality, precautions are recommended, including avoiding swimming near affected areas. Check beach water testing results before heading to the water after a storm.
Understanding inflow and infiltration
Two separate processes — inflow and infiltration — send excess water into the sanitary sewer system, with consequences similar to a combined sewer overflow. However, this water also has to be collected, transported and treated alongside real sewage, which strains treatment capacity, limits growth and drives up costs for everyone who pays taxes.
Inflow
Water that enters the sewer system directly from sources such as roof leaders, foundation drains, yard drains, catch basins and cross-connections between storm and sanitary sewers, particularly during rain events.
Infiltration
Groundwater that seeps into the sewer system through cracks, defective pipe joints, faulty connections or deteriorating maintenance holes, often a sign of aging infrastructure.
What you can do
Small actions at home can make a meaningful difference in reducing overflow volumes across the system. If you experience basement flooding, contact your city or town.
Disconnect your downspouts
Redirect downspouts away from the sewer system and onto your lawn, garden or into a rain barrel for later use.
Avoid use during wet weather
During heavy rain or snowmelt, avoid running dishwashers, washing machines or flushing toilets more than necessary to reduce the load on the sewer system.
Wash your car wisely
Use a commercial car wash where water is recycled. Or, wash at home over grass or gravel with biodegradable soap so water drains into the ground rather than the sewer.
Install low-flush toilets
Reducing household water consumption lowers the volume of wastewater entering the system, helping maintain capacity during wet weather.
Install a rain barrel
Collect rainwater from downspouts to water plants and grass. This reduces runoff that would otherwise enter the sewer system.
Watch for root damage
Tree roots can crack and infiltrate aging sewer pipes on your private property. Be aware of mature trees near your lateral sewer line and inspect pipes if you suspect damage.
Combined Sewer Overflow Control Program
The Combined Sewer Overflow Control Program is a cost-share program between Niagara Region and local municipalities that funds projects to reduce the amount of stormwater entering the sanitary system. This reduces basement flooding, environmental overflows and frees up system capacity.
Types of projects
Studies
Investigative work to assess infrastructure condition and identify where excess stormwater is entering the system, using flow monitoring and other tools.
Sewer separation
Installing new storm sewers to separate combined systems so that stormwater and sanitary sewage travel through different pipes.
Storage tanks
Large underground tanks store excess wastewater during storms. Once capacity is restored, the wastewater is pumped back into the system for treatment.
| Date of overflow | Volume (1 megalitre = 1 million litres) |
Reason for overflow |
| May 22, 2025 | 27.080 ML | Heavy precipitation |
| April 2, 2025 | 39.168 ML | Heavy precipitation |
| March 6, 2025 | 6.115 ML | Heavy precipitation |
Biggar Lagoon Sewage Pumping Station
| Date of overflow | Volume (1 megalitre = 1 million litres) |
Reason for overflow |
| April 2, 2025 | 3.263 ML | Heavy precipitation |
| March 6, 2025 | 0.064 ML | Heavy precipitation |
| Date of overflow | Volume (1 megalitre = 1 million litres) |
Reason for overflow |
| Oct. 30, 2025 | 2.731 ML | Heavy precipitation |
| May 22, 2025 | 4.603 ML | Heavy precipitation |
| April 2, 2025 | 14.308 ML | Heavy precipitation |
| March 5, 2025 | 1.815 ML | Heavy precipitation |
Old Orchard Sewage Pumping Station
| Date of overflow | Volume (1 megalitre = 1 million litres) |
Reason for overflow |
| June 18, 2025 | 1.713 ML | Heavy precipitation |
| May 22, 2025 | 0.370 ML | Heavy precipitation |
| April 2, 2025 | 4.359 ML | Heavy precipitation |
Woodsview Sewage Pumping Station
| Date of overflow | Volume (1 megalitre = 1 million litres) |
Reason for overflow |
| June 18, 2025 | 0.810 ML | Heavy precipitation |
| April 2, 2025 | Not available | Heavy precipitation |
Historical overflow data
2024
Total overflows: 7
Total volume: 53.153 ML
2023
Total overflows: 30
Total volume: 54.866 ML
While the volume of an overflow may seem large, the amount of untreated sewage present in the overflow is small when compared to the amount of stormwater or snowmelt.
Niagara Region typically treats about 80,000 megalitres of sewage each year. The vast majority of wastewater discharged into the sewer system receives full treatment and only a small percentage of this sewage overflows. These overflows usually only occur during periods of heavy rain or during seasonal snowmelts.