65 Harwood Ave. S. Ajax, Ontario L1S 2H9 Joanne.dies@ajax.ca Tel. 905-619-2529 ext. 3373


Duffin Creek Water Pollution Control Plant (sewage plant)


This sewage plant is the 2nd largest in Canada currently flushing 340 million litres (MLD) of treated sewage per day into the lake.  The town of Ajax has seen a steady increase in algae along its shores since the third expansion to the plant in 2006.  This expansion increased the plants capacity to treat and flush 620 MLD  into the lake.


The sewage plant is owned and operated by the regions of Durham and York with 80% of sewage coming from York Region through the “Big Pipe”. The Regions share the costs at 20%  Durham Region and 80% York Region.


While the plant effectively treats raw sewage, it does not remove phosphorus which feeds the algae. Increasing the volume of treated sewage from 340 – 630 MLD allows phosphorus to nearly triple.  A future planned 4th expansion to the plant would see an potential increase of 1 billion litres a day.

In short, phosphorus from the plant is over-fertilizing the nearshore water of Lake Ontario causing the proliferation of nuisance algae to grow, resulting in a series of unacceptable environmental impacts including interference with spawning by native fish species and, the potential destruction of fish habitat.


During the summer, the algae breaks off from the lake bottom, washes to shore and rots. The nauseating odour of rotting algae prevents families from enjoying their back yards or simply opening their windows.  Some people experience a physical reaction such as nausea and headache.

It also prevents families and visitors from enjoying the trails, beaches and waterfront park that Ajax has worked to protect for public use


The Regions failure to acknowledge that the plant is the point source of phosphorus means they also fail to acknowledge the environmental impacts such as;

  • Odour
  • Algae has covered  fish spawning areas on the near shore resulting in increased egg exposure and predation.
  •    Avian Botulism, a threat to birds that feed on small animals on decomposing algae mats that contain a bacteria which can kill them.
  •   Future threat of our drinking water.

June 2021 the Province announced it’s consideration of twinning the big  Pipe from upper York Region to the Duffin’s Creek Sewage Plant. Shelving York’s State of the Art solution for Lake Simcoe. This may result in the 4th expansion to the plant being built sooner than anticipates.

Twinning the pipe would provide more capacity for development and result in more effluent being discharged into Lake Ontario. It would also require tertiary treatment to protect our water quality for future generations.

The Region of Durham support this treatment as the plant expands. A this time the province has not announced their decision.