The Regional Municipality Of York


Duffin Creek Water Pollution Control Plant

The Duffin Creek Water Pollution Control Plant is a top performing wastewater treatment facility located on the shores of Lake Ontario in the City of Pickering. It treats wastewater from 80% of the residents and businesses in The Regional Municipality of York and from all of the residents and businesses in the Town of Ajax and City of Pickering in The Regional Municipality of Durham.

This wastewater treatment facility is part of the York Durham Sewage System and is a result of the province’s long-term vision to grow and service these two municipalities.

Duffin Creek Plant Outfall Environmental Assessment Approved

On Thursday, November 7, 2019, the Regional Municipalities of York and Durham received a decision on the Outfall Environmental Assessment (EA) from the Minister of the Environment, Conservation and Parks (MECP). The Minister’s decision noted that an individual EA is not required. The Minister identified specific conditions to ensure additional scientific work and consultation is undertaken as the Regions move ahead with the modifications to the outfall pipe, begin operational enhancements and implement improvements to proposed treatment (per the Class EA and PRAP) at the Duffin Creek Plan. For more information on the Duffin Creek Plant Outfall EA and how we are meeting the Minister’s conditions, visit

Plant History: Then and Now

Built in the 1970’s by the Province of Ontario, ownership of the Duffin Creek Plant transferred to York Region and Durham Region in 1997. Since then, the two Regions and the provincial and federal governments have invested more than $850 million in new technologies, equipment, training and best practices to ensure the Duffin Creek Plant continues to protect our waterways and local environment.

As a result of this ongoing investment, the Duffin Creek Plant has one of the best performance records of all wastewater plants on Lake Ontario.

Read more about the Duffin Creek Plant’s exceptional performance in the 2018 Duffin Creek Sustainability Report.


Outfall Pipe EA History


In 2010, York and Durham Regions began a Class Environmental Assessment (Class EA) recommending the improvement of existing processes at Duffin Creek Plant to increase treatment capacity to at least 630 megalitres per day. This Class EA was completed and released for public comment in November 2013.

Following requests to elevate the Class EA to an Individual EA, the Regions completed a Phosphorous Reduction Action Plan (PRAP) in 2018 to address questions. The PRAP was then submitted to the province for review.

In November 2019, the province denied the elevation requests and applied additional conditions on the project. This decision allows the Regions to move ahead with the modifications to the outfall pipe along with proposed treatment and operational enhancements (outlined in the Class EA and PRAP) at the Duffin Creek Plant.

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What is the Duffin Creek Phosphorus Reduction Action Plan Study?

Duffin Creek Phosphorus Reduction Action Plan Study

On April 4, 2016, the Minister of Environment and Climate Change required York and Durham Regions to undertake a Phosphorus Reduction Action Plan (PRAP) Study at the Duffin Creek Water Pollution Control Plant (Duffin Creek Plant). After 18 months, the PRAP Study is now complete.

The purpose of the PRAP Study was to research:

  • The level of phosphorus removal the Duffin Creek Plant can achieve with its current wastewater treatment processes (referred to as “secondary treatment”)

  • The level of phosphorus removal the Duffin Creek Plant can achieve with additional wastewater treatment stages that would have to be built (“tertiary treatment”)

  • Assess the feasibility of reducing effluent phosphorus during the seasonal algae growth window, April through August each year

Results of the PRAP study are available to the public, along with more information about the Duffin Creek Plant in Pickering, at the project website Residents had the opportunity to view the report and provide comments to the Ministry of Environment and Climate Change from January 10, 2018 to February 23, 2018.

  • York and Durham Regions rely on Lake Ontario as a raw water source for the drinking water for most of their residents and business. Protecting the quality of the lake water for today and future generations is a corporate priority.

  • Duffin Creek Plant treats wastewater from 80 percent of the residents and businesses in York Region, as well as residents and business in the Town of Ajax and City of Pickering in Durham Region.

  • With over $850 million in upgrades in the past 10 years, the Duffin Creek Plant is a top-performing wastewater treatment facility located on the shores of Lake Ontario in the City of Pickering.

  • For more than a decade, the Duffin Creek Plant has been blamed for causing excessive algae growth at the Ajax waterfront by discharging phosphorus into the water.

  • Over the past 10 years, peer-reviewed science (such as the Journal of Great Lakes Research) has shown there are many factors causing excessive algae growth in the Great Lakes, with a lake-wide study showing Duffin Creek Plant to be responsible for just 1.1 percent of the phosphorus in Lake Ontario. Most studies conclude that surface runoff (from rivers, streams and storm sewers) is the major contributor of phosphorus to the lake.

  • At the expense of taxpayers, the Town of Ajax is petitioning the Province to have York and Durham Regions spend more than $200 million to upgrade the Duffin Creek Plant with Tertiary Treatment technology within the next five years, believing this will solve the waterfront’s algae problem. Investing $200 million to reduce a 1.1 percent phosphorus contribution will not eliminate Lake Ontario’s algae problem.

  • York and Durham Regions care about the environment and rely on Lake Ontario for drinking water. Together the Regions are part of several national, international and provincial water and waste associations and research organizations that monitor environmental impacts and research effective best practices and technologies to improve our environment.

  • Over the past 15 years the Regions have invested over $15 million in wastewater studies and water quality monitoring around the Duffin Creek Plant through environmental assessments and plant optimization studies.

  • Further funding is included in each Region’s budget to continue the important work of maintaining our wastewater treatment plant and monitoring Lake Ontario’s water quality.

  • On January 10, York and Durham Regions submitted a scientifically sound and cost-effective Action Plan to the Ministry to reduce the Plant’s phosphorus levels. This Action Plan involves optimizing the Plant’s treatment process to help further reduce phosphorus levels in the treated water flowing back into Lake Ontario without requiring Tertiary Treatment or $200 million.

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Process and Performance


The Duffin Creek Plant has an underground outfall pipe that extends more than one kilometre under the lake bed into the deeper waters of Lake Ontario. At the end of the outfall pipe, nozzles extend above the lake bed and release treated, clear and disinfected water into Lake Ontario.


The Duffin Creek Plant is the most highly regulated treatment plant discharging to the open waters of Lake Ontario. Among its benefits, it has the strictest phosphorus concentration compliance limits of all large treatment plants in the GTA.

Ten years of sampling confirms the high quality of Ajax-Pickering nearshore waters: Experts have found the phosphorus levels in the Ajax-Pickering nearshore are better than many cottage lakes, better than Ministry of the Environment and Climate Change targets and better than the existing target under Canada/United States agreements on open-water phosphorus concentrations.

Duffin Creek does not bypass treatment processes: Apart from the Duffin Creek Plant, most large GTA treatment plants will bypass treatment processes in response to increased wastewater flows occurring during rainstorms and intense snow melts. This means that untreated or only partially treated wastewater flows is released from a treatment plant. It has been estimated a billion litres of non-treated or partially-treated sewage flows into Ontario’s rivers and lakes each year from bypass events.  The Duffin Creek Plant uniquely doesn’t bypass treatment.

Duffin Creek is a minor contributor of phosphorus to the Ajax-Pickering nearshore: On average, up to 94 per cent of the total phosphorus entering the Duffin Creek Plant in the wastewater is removed during the treatment process. Lake Simcoe and other Great Lakes research proves there are many sources of phosphorus including ambient levels of phosphorus in the lake, rivers and, tributaries, stormwater runoff, air borne contribution from  dust during and farming operations. Locally, these other sources contribute many times more phosphorus to the Ajax-Pickering nearshore than the treatment facility.

Read the Environmental Commissioner of Ontario’s 2017 Report: Good Choices, Bad Choices to learn more about how phosphorus ends up in our lakes.

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Phosphorus Facts

Phosphorus is a nutrient found in every living organism and makes up one per cent of the human body.  Phosphorus in wastewater comes from humans, food waste, fertilizer, dishwashing and laundry detergents, household cleaners and numerous commercial and industrial products released into the sewer system. It is also found in soils and sediments, plants and animals. The Duffin Creek Plant removes on average, up to 94 per cent of phosphorus from wastewater arriving at the plant and disinfects it before releasing clear treated water into the open waters of Lake Ontario.

Like people, a lake requires many nutrients in proper amounts to stay healthy. In the Great Lakes, phosphorus is a nutrient that has a great influence on the health of lake ecosystems. Invasive mussels, temperature, light sources and high phosphorus levels are just some of the factors leading to algae growth and affecting the balance of the ecosystem of the Great Lakes.

Since 2008, Duffin Creek’s new treatment processes have reduced the amount of dissolved phosphorus exiting the facility. This amount will continue to decrease in the future, even though wastewater volume will increase due to population growth.

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Cladophora Algae Frequently Asked Questions

What is Cladophora?

Cladophora is a branching aquatic plant that grows in spring and summer and can measure over a metre tall.

It is a fibrous aquatic plant forming long visible threads called filaments; this filamentous algae intertwines and resembles wet wool, attaching to bedrock and the lake bottom.

What causes Cladophora to grow?

Growth depends on soluble reactive phosphorus that is present in near shore lake water. The higher the soluble reactive phosphorus, the higher presence of algae.

Soluble reactive phosphorus comes from many sources, including:

  • Natural forms in lake water
  • Runoff from streams, lawn and farm fertilizers
  • Airborne sources (e.g., dust)

Invasive mussels provide a further source of soluble reactive phosphorus by filtering  suspended particles containing phosphorus and converting particulate phosphorus to soluble reactive phosphorus which Cladophora needs for growth.

Filtration by invasive mussels clarifies the water allowing sunlight (also essential for Cladophora growth) to penetrate to greater depths, thereby extending the area in which it can grow.

Why is Cladophora a problem?

When all of the growth conditions are in place, Cladophora can accumulate as a dense growth of plant material in the nearshore of lakes.

In late summer, Cladophora growth breaks off (sloughs) from the lake bottom with wave action during late summer storms. Lake currents can carry masses of plant growth ashore where it accumulates on shorelines and clings to rocks and shoreline vegetation. The decomposing plant material can cause a temporary odour problem.

What are the leading causes for this resurgence?

  • Increased light penetration increase the habitat for Cladophora growth by extending the depths in which it can grow
  • Through their natural filtration, invasive mussels have made the lake water more clear, thereby increasing habitat and are also a new source of soluble reactive phosphorus in the nearshore zone causing greater growth
  • Increased soluble reactive phosphorus allows greater growth at shallower depths
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Leadership in Environmental Energy and Design (LEED) Gold

The Duffin Creek Plant dewatering facility has been recognized for design excellence. The facility, which separates water from solids, has the distinction of being the first wastewater treatment building in Canada to achieve LEED Gold Certification for excellence in environmental building design.

Energy Recovery

The Duffin Creek Plant uses recovered energy from incinerators to generate steam used to power turbines at the treatment plant. Ash left from the incineration phases of treatment is sent to St. Mary’s Cement and used to create cement products.

Recipient of Wildlife Conservation Award

York and Durham Regions worked closely with the Toronto and Region Conservation Authority to create a Greening/Biodiversity Plan. This plan is recognized by the Wildlife Habitat Council for its achievement to maintain the Wildlife at Work Program. Improvements to the area include a natural sanctuary for small animals, ponds, native plants and a newly constructed wetland.

High scores from EcoJustice

In the most recent (2013) Great Lakes Sewage Report Card produced by EcoJustice, the Duffin Creek Plant received an overall B+ grade. This prominent ranking reflects the engineering excellence that has gone into the treatment facility and the Regions’ respect for the environment.

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Last updated: January 28, 2020

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