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Second Marsh

Marsh Background

Oshawa Second Marsh is a 137 ha provincially significant coastal wetland that provides considerable habitat for wetland dependent wildlife. It is particularly known as an important breeding and migratory stopover area for birds. From the 1930’s to the 1970’s significant impacts to the marsh including pollution, sedimentation and habitat loss occurred as a result of dredgeate deposits from Oshawa Harbour, upstream urbanization, development of adjacent lands, and effluent from a water treatment plant. Between the 1960’s and 1990’s there were several ownership changes, a proposal to turn the marsh into a port, and prolonged studies and battles to save the marsh. During this time the original western outlet was dyked causing the beach to blow out on the east side, which was followed by a wash out of vegetation and significant sediment deposition. In the 1990’s ownership of the marsh was returned to the City of Oshawa and a Marsh Management Plan was developed in 1992.

Management and Restoration Actions

Following the development of the Marsh Management Plan (1992) Phase 1 of the restoration works began. This included moving the outlet back to the west side of the marsh; installing flow deflection islands, native plantings, and carp barriers; and the establishment of trails, lookouts, and signage.

While these actions provided some benefits to the marsh it was determined that further action was needed and a Marsh Management Strategy was developed in 1999. This initiated Phase 2 of restoration which included the construction of an earthen dyke to divert the creek around the marsh, installation of a fish passage structure and installation of a 2-way pump. Subsequently the marsh was drawn down in 2004 which mimicked low water levels not seen since before Lake Ontario water level regulation. This acted to expose the seedbank, stimulate vegetation growth and improve water quality.


The Marsh Management Steering Committee is composed of members from the City of Oshawa, Ducks Unlimited Canada, the Friends of Second Marsh, Central Lake Ontario Conservation and Environment Canada. The City of Oshawa is responsible for operational management and organization of the Marsh Management Steering Committee. Ducks Unlimited Canada is responsible for marsh restoration works, Friends of Second Marsh for education, interpretation and stewardship, and Central Lake Ontario Conservation and Environment Canada for environmental monitoring. There are also many volunteers without whose help many of the monitoring, stewardship and restoration initiatives would not have been possible.

City of Oshawa

Through ownership of the Oshawa Second Marsh, the City of Oshawa can ensure the responsible management and conservation of the marsh, provide the public with access and connection to the natural heritage features along the waterfront, as well as promote and maintain the social, cultural, economic, and environmental benefits associated with marsh.

By maintaining partnerships within the steering committee the City of Oshawa gains expertise and financial support in the successful management and rehabilitation of the marsh, ensures a healthy ecosystem which supports and reduces the impacts on municipal infrastructure and private property, and facilitates the sustainable management of the marsh into the future.

Ducks Unlimited Canada

Restoration projects implemented by Ducks Unlimited Canada provide valuable improvements to the marsh including improved water quality, diversity and quality of wetland vegetation, quality of habitat for fish and wildlife, and recreation and nature appreciation opportunities. The infrastructure that they have put in place helps to keep out invasive carp and enables drawdowns to mimic pre-regulation water level fluctuations to promote a more natural, dynamic, healthy wetland.

Friends of Second Marsh

Part of the mandate of Friends of Second Marsh is to enable the community to enjoy the natural heritage the wetland provides, while safeguarding it at the same time. Friends has developed and implemented the CUE principle (Caring comes from Understanding comes from Experiencing) to nurture a sense of stewardship in members of the community. Opportunities to experience the wildlife area are provided in a number of ways including an extensive trail system for hiking, boardwalks to protect sensitive ecosystems, and lookouts to provide views of the wetland and surrounding area. In order to provide people with some up close, hands-on experience with nature, a number of interactive programs, for both students and the public, are run at various times throughout the year. By necessity, part of the safeguarding effort also involves restricting certain activities in certain regions of the wildlife areas so as to protect sensitive ecosystems and wildlife species.

Central Lake Ontario Conservation (CLOCA)

The monitoring work conducted by CLOCA and Environment Canada is essential to establish baseline conditions and assess the ecological conditions and overall health of the marsh. As a result of this work, there is a long-term dataset that enables the detection of changes over time and identification of trends. We are also able to identify Species at Risk and Species at Risk habitat, and identify invasive species presence and extent. All of this information is used to determine restoration & management needs and support education & stewardship initiatives. Ongoing monitoring allows for the assessment of the success of restoration actions.

Monitoring results showed a marked improvement in biological conditions in the years following the initial drawdown in 2004. However, this was followed by a gradual return to open water conditions more recently. In that time monitoring has also shown the establishment and spread of several invasive species including Common Carp, Goldfish, Common Reed, European frog-bit, and Flowering Rush. Wildlife community and water quality conditions now indicate that another drawdown is required to mimic low water levels that occurred historically.


The Marsh Management Steering Committee has made the following recommendations given the current state of Oshawa Second Marsh:

  • Initiate another drawdown in 2015 to stimulate vegetation growth and improve water quality.

  • Resume monitoring.

  • Improve the carp gate to prevent carp from gaining access to the marsh and to prevent vandalism or removal of the gate.

  • Map the extent of invasive plant species and develop management plans for all invasive species present.

  • Establish and enforce rules for access and fishing in the marsh. Improve awareness through signage.

  • Continue to maintain and improve infrastructure.

  • Increase public awareness and understanding so that public can enjoy the wetland without negatively impacting it.


Following the implementation of the recommendations, the Committee expects to see the following actions and improvements:

  • Drawdown of the marsh from May to October 2015. This exposes the seedbank stimulating vegetation growth, improving water quality and reducing the invasive fish population.

  • Monitoring post drawdown to assess the re-establishment of emergent vegetation and extent of invasive species to determine the success of the drawdown in improving biological communities and water quality.

  • Improved carp gate that prevents adult carp from gaining entry to marsh.

  • Implementation of management actions to control invasive plant species.

  • Well-used infrastructure that is safe and accessible.

  • Increased appreciation and awareness of wetland and reduced impacts by user groups.

Drawdown Rehabilitation Project

The Oshawa Second Marsh watershed is highly influenced by human activity and its surrounding land use.  Watershed inputs, stream bank erosion, invasive species, and regulated water levels on Lake Ontario, impact water quality and quantity within the marsh.  The changing nature of the wetland due to these external influences requires ongoing management and monitoring to ensure the health of the ecosystem.

Since the City of Oshawa obtained ownership of Second Marsh in the 1990s, a number of successful restoration and rehabilitation projects resulted in an improvement of the health and diversity of the marsh.  The most successful restoration project occurred in 2004 when water levels within the marsh were mechanically lowered (drawndown) and allowed to naturally recharge (flood).   The drawdown was very successful in improving the overall health and diversity of the marsh.

Recent results of ongoing monitoring show that the marsh needs another helping hand to improve water quality and the impacts of non-native invasive species such as Common Carp, Goldfish, Phragmites, European Frog-bit and Flowering Rush. More information regarding the identification and impacts of these invasive species can be found at

Restoration Project

To preserve the health of Second Marsh, in spring 2015, the City of Oshawa, Central Lake Ontario Conservation Authority (CLOCA), Ducks Unlimited Canada (DUC) and Friends of Second Marsh will be drawing down the marsh water level to stimulate vegetation growth by exposing the plant seeds in the mudflats to sunlight.  The drawdown will mimic natural conditions that historically occurred in Lake Ontario during alternating periods of high and low water levels.

The drawing down of water levels is a best management practice used to optimize the health and diversity of wetlands by kick starting biological activity. The drawdown is expected to produce similar success as the previous drawdown including:

  • stimulate seed germination, root development and increased vegetation growth and diversity;

  • release nutrients locked in the marsh muck;

  • improve water quality by reducing turbidity; and

  • improve fish habitat and fish community while reducing invasive fish population such as common carp and goldfish.

By mimicking natural conditions the project will ensure that the marsh continues to remain healthy and productive long into the future.

Once the vegetation is established in September, re-flooding will bring water levels back to their seasonal average. This is perfect timing for the fall migration of many waterfowl, shorebirds, raptors and songbirds as they look for staging areas like Second Marsh to feed and rest.

Project and Timeline

Visitors will notice changing conditions within the marsh over the coming year. The changes are typical of natural conditions that would have been seen prior to human influences. Throughout the project, visitors will see an abundance of local and migrating waterfowl, shorebirds, raptors, songbirds and other wildlife to attracted to the mudflats to feed and rest.  Keep your eyes on the marsh throughout the entire drawdown process for some great wildlife viewing opportunities. A number of viewing locations can be found along the Waterfront Trail where users are encouraged to take pictures to help us document the changing conditions throughout the process.

Spring 2015

  • Pumping will begin approximately the 3rd week of April once the ice melts.

  • It will take approximately 4 weeks to pump the water out with a target date of May 31st at the latest to ensure optimal conditions for re-vegetation.

  • Starting in the spring visitors will  see very dry conditions known as mudflats  attracting shorebirds in the spring and summer, right through to reflooding.

 Summer 2015

  • The dry conditions are necessary to allow for natural germination of vegetation.

  • Monitoring of vegetation growth and site conditions will occur during the summer months.

  • If necessary additional pumping out after heavy rains or the pumping in of water to irrigate new growing vegetation may occur during this period.

  • Improvements to the carp gate will be made to prevent the invasive species from accessing the marsh and to prevent vandalism.

Fall 2015

  • Re-flooding, either passively if lake levels are sufficient or by pumping, will begin in late September to bring water levels back to their seasonal average.

  • Water levels will be kept shallow in order to prevent overwinter drowning of newly germinated aquatic plants.

Spring 2016

  • Water levels will begin to increase to a level that supports vegetation growth

Fall 2016

  • Water levels will increase to normal levels, improving water quality and attracting local and migrating waterfowl, shorebirds, raptors, songbirds and other wildlife to feed and rest.


Over the course of the drawdown and on an ongoing basis, monitoring of the health of Second Marsh will continue and be reported as part of the Durham Region Coastal Wetland Monitoring Project (DRCWMP). The DRCWMP, which monitors water quality, fish and bird community, frog/toad community, submerged aquatic vegetation and aquatic macro-invertebrates within the marsh, will continue to provide valuable information on the condition and health of the marsh.  Monitoring through the DRCWMP will allow for continued adaptive management moving forward.

Photo Contest

Help us document the draw down process and you could win an outdoor prize pack!

To enter, simply take photos of the marsh and share them with us at or post on social media with the hashtag #SecondMarshHelpingHand.  Contest closes October 15, 2015.

Frequently Asked Questions

Why does the water need to be drained from the marsh?

Alternating periods of high and low water levels that naturally occurred historically in Lake Ontario supporting the health and a high diversity of habitat within Second Marsh. Since 1960, water levels on Lake Ontario and the St. Lawrence River have been artificially managed removing the periods of very low and very high water levels. This has generally resulted in the loss of wetland habitat, structural complexity, and species diversity within many coastal wetlands along Lake Ontario.

The drawing down of water within wetlands is a common tool used in wetland rehabilitation projects.  It mimics historic natural coastal conditions that help to maintain a healthy and productive wetland ecosystem. Low water levels provide optimal conditions for the germination of a diverse array of wetland plants, which supply food and habitat to a variety of wildlife.

As more water is held in the marsh, the productivity of plants and invertebrates also increases, providing an abundant food source important to many wetland dependent species, including waterfowl.

What will happen to the fish and aquatic life in the marsh during the drawdown?

Resident species are well adapted to dynamic changes in water levels that occur naturally in marshes. It is important to note that deeper areas within the marsh will not be drained completely allowing refuge habitat for various species including fish, reptiles and amphibians and invertebrates. Pumping will gradually lower the marsh water level over a number of weeks allowing fish to move into these refuge areas.

How will the water be removed?

The drawdown will utilize an existing electric pump installed during the first successful drawdown in 2004.  The pump will operate for approximately 4 weeks depending on site conditions, spring rains, etc.  During this time, most of the water will be pumped out of the Marsh, except for a deeper portion in the southeast portion of the marsh.

How long will it take for the water to be removed and the health of the Marsh to improve?

The process for drawing down water levels and reflooding mimics natural low and high water conditions that occur seasonally over one year cycle. Based on the outcome of the previous drawdown at Second Marsh, the health of the marsh will improve within the first and second year.  In general, water will be out of the marsh from May to September. During this time, dormant seeds of aquatic plants will germinate, creating a green carpet of new growth across the marsh. Nutrients will be released from decaying old plant material.

Ongoing habitat assessment and other monitoring will determine future management programs.

What approvals are needed to do this work?

To undertake the project the following approvals have been obtained:

  • Approval for Alterations to Shorelines and Watercourses - CLOCA
  • Permit to Take Water – Ministry of the Environment
  • Species at Risk Act – Ministry of Natural Resources
  • Fisheries Act – Department of Fisheries and Oceans

How will the project be funded?

The drawdown is funded by Ducks Unlimited Canada and through in-kind field support provided by the City of Oshawa, Friends of Second Marsh and CLOCA.


For more information on Second Marsh drawdown Salisha Price, Supervisor, Parks Development, Technical and Community Support at 905-436-3311 ext. 2374.