Swan Lake Water Quality

Swan Lake

Site Description

 Swan Lake is situated in the City of Markham at the intersection of Sixteenth Avenue and Williamson Road. A gravel pit in the 1960s and 1970s, Swan Lake, is currently a community feature near the heart of Historic Markham Village, surrounded by multiple trails, a playground and urban development.

Water Quality

Given that Swan Lake is an old gravel pit, the water in the Lake tends to be very stagnant, which has led to poor water quality, and there have been reports of water quality issues since the area around the Lake was developed in the mid-1990s.  In 2012, the City initiated a monitoring program of the Lake to measure and monitor the water quality.  Due to high phosphorus and other nutrient levels, significant algal blooms were present during the summer months.

Council authorized a chemical treatment to help improve the Lake water quality, and in 2013, 25 tonnes of Phoslock was applied across the Lake. Phoslock treatment resulted in a 60% reduction in total phosphorus in the surface and mid-layers of the Lake and increased water clarity.

Unfortunately, over time, the City expects that nutrient levels in the Lake will rise again due to the presence of Canada Geese.  The City has initiated a geese control program in order to minimize the geese present in the park.

In 2020, the City developed a water quality improvement strategy for Swan Lake and Council supported the study recommendations, including a chemical treatment program starting in 2021. A long term plan for chemical treatment will be presented to Council in 2021.

Phoslock: A non-toxic clay product capable of removing phosphorus from the water and capping phosphorus in the bottom sediment.


Annual Monitoring Program

Water quality monitoring of Swan Lake has been conducted annually since treatment in 2013 to track water quality and the continued effectiveness of the Phoslock. The ongoing monitoring program allows for continuous assessment of the water quality in Swan Lake and will be used to help establish a long-term plan for water quality improvement in Swan Lake.


Algal Bloom and Toxicity 

High nutrient concentrations, and a lack of sufficient water circulation in Swan Lake, has resulted in the growth of different groups of algae, including green algae, diatoms and bluegreen algae (a.k.a. cyanobacteria).  Blooms of cyanobacteria are not only unsightly when they form scums on the Lake surface, but they may also produce toxins such as Microcystins, which is toxic to humans, pets, and wild animals upon contact or ingestion. 

While the presence of blue-green algae is rare, the City has restricted access to the Lake as a precaution.  Residents and/or their pets should not enter the Lake. 


Geese Control

Geese are the primary external source of nutrients in the Lake. Therefore, active geese management is completed annually. The geese control program started in 2014, focusing on resident geese. The program extended to the management of migratory geese in 2016.  While the waterfowl number in Ontario has been reported to have doubled over the last ten years, the Swan Lake geese population has decreased since the inception of the geese control program, indicating the efficacy of the program.

 In 2020, the City reviewed additional geese management measures in consultation with subject matter experts and area residents. Council approved additional hazing and the installation of nine strobe lights to be implemented immediately. 

A Volunteer program was also initiatives through which residents can submit observations about the geese present at the Lake through an online survey. For more information on how to collect and submit geese counts, please see these instructions. 

Data collected by the City contractor and volunteers have so far indicated that the geese numbers have decreased due to the program enhancement. 


Council Reports

Report Date Link
Update on Swan Lake Water Quality February, 2013 Report
Swan Lake Water Quality Improvement Program June, 2020 Presentation
Geese Management at Swan Lake: Overview of Options and Path Forward September, 2020 Presentation 

For more information, please contact:

Rob Grech, Manager, Stormwater
Email: rgrech@markham.ca       Phone: 905.477.7000 x 2357

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