Combined sewer overflows (CSOs)

During heavy rainfall, sewer pipes and wastewater treatment plants can get overwhelmed as they have a limited capacity and cannot manage all the additional rainwater.

When this happens, CSOs occur because the combined sewers direct excess rainwater runoff and untreated sewage into receiving waterbodies around Vancouver –  like False Creek, the Fraser River, and Burrard Inlet -  to prevent the wastewater treatment plants and pipes from flooding. 

In dry weather or light rainfall, sewage is carried to a wastewater treatment plant where it is treated prior to release.

Sewage includes all water that goes down the drain from household, industrial, and commercial activities. However, rainwater often makes up a much larger volume than sewage.

Protecting public health and the environment

The sewer system was originally designed to allow CSOs in order to protect public health and the environment by preventing treatment plants or buildings from getting flooded.

We have been working towards eliminating CSOs for many decades, and since 2002 it has been a provincial requirement.

Our primary strategy for eliminating CSOs has been through sewer separation which replaces combined pipes with separate pipes for sewers and drainage. We are now also incorporating green rainwater infrastructure to help achieve our goal. 

CSO outfall locations

Sewer outfalls vary in size and location depending on the specific design requirements. Some are visible during low tide and others are always underwater.

CSO outfalls are located throughout Vancouver’s shorelines. The locations of City of Vancouver-owned CSO outfalls are shown on the map below.

Information for recreational water users

Follow personal safety precautions for swimming in Vancouver waterways.

Before swimming in any natural waterbody, refer to Vancouver Coastal Health for information about water quality at beaches, current swim advisories, and precautions you can take.

How you can help protect our waterways

  • Keep trash out of yards and streets where it can be swept into adjacent waterways by rain or melting snow.
  • Don’t pour chemicals down the drain, on the ground, or into catch basins. This could contaminate the soil, groundwater, or nearby surface water. Motor oil, household cleaners, medicines, and other household products contain hazardous or toxic substances that can contaminate ground or surface waters.
  • Wash your laundry in cold water to reduce the number of microfibres that are shed from our laundry and improve the health of our oceans. Microfibres from our laundry are one of the largest sources of microplastic pollution in the ocean.
  • Adopt a catch basin in your neighbourhood. Before a rainfall, clear your catch basin of debris and litter to prevent it from washing into adjacent waterways or entering our sewer system.
  • Pick up after your dog. Feces from animals like dogs and geese can get picked up by rainwater and sent into nearby waterways contributing to high E.coli levels in waters and swim advisories on beaches.

Healthy Waters Plan

Learn about Vancouver's long-range sewer and rainwater management plan.

Separating sewage from rainwater

We are working toward the Province of BC's environmental goal to eliminate sewage overflows.

Adopt a catch basin

Help prevent flooding in your neighbourhood, adopt a catch basin to care for.