NOTICE - Aquatic Weed Control in Collingwood Harbour

July 6, 2020
Parks, Recreation, & Culture

Please take notice that there will be aquatic weed control measures taking place on Wednesday, July 8 in the Collingwood Harbour Launch Basin and the Yacht Club Basin.
This will be a chemical weed control application that will combat weed growth in the water. 

  • Please do not use the water for animal consumption and swimming for 24 hours after completion of the chemical application.
  • Please do not use the water for human consumption and irrigation for 5 days after completion of the chemical application  

The contractor applying the chemical weed control has a permit from the Ministry of the Environment. Signage will be in place at both Basins. Thank you for your patience and understanding as we control aquatic weeds in the Harbour.

Please submit any comments or concerns to the Acting Director of Parks, Recreation, and Culture, Mel Milanovic at
For more information, contact:
Green Stream Lawn and Vegetation Management Inc. 200 North Service Road West, Suite 476, Oakville, Ontario, L6M 2Y1, 905-510-1229

Additional Information:
Since the early 2000’s, it has become clear that Collingwood Harbour has a problem with aquatic weeds, a situation consistent with other harbours in Lake Huron and Georgian Bay. The areas involved include the Collingwood Yacht Club basin and the Town’s launch ramp basin south of the Ferry dock. The thick growth of weeds that prevents swimming and safe boating is seldom found where depth exceeds 10 to 12 feet.

The primary problem aquatic weed is Eurasian Milfoil, a submergent invasive species rooted in the bottom and producing long upward stalks that can grow to over 9 feet long. They can grow so thick that it chokes out the natural weed (elodea and coontail) and creates problems for sport fish in the area. These weeds cause significant problems for motorized boats and sailboats, wrapping up in propellers or entangling deep keels and rudders.

In 2012, the Parks, Recreation, and Culture department completed a Staff Report on this topic and explored the various options available for control of the weeds in the Harbour. Chemical control was the recommended option based on many factors considered. Chemical controls work by utilizing a chemical that is applied and falls through the water column and affects the weeds directly below the application area. The chemical begins to degrade after application and is inert within a day or so. The chemical is designed to affect only vegetation and does not harm the fauna in the affected area. The weeds usually die in about three days and fall to the bottom of the harbour. The window for spraying in our area is in early to mid July in order to ensure fish hatching is complete and the fry are able to move about.

The product to be used is called REWARD. It is a non-volatile aquatic herbicide and the active ingredient is diquat ion. It is a registered product with the Pest Control Products Act and can only be applied by a licensed aquatic exterminator/operator. It presents no hazard to fish, other aquatic life or animals and humans when used as directed. REWARD is inactivated upon contact with soil, mud, or lake bottoms; therefore, it has no residual herbicidal effect.