Environment

Between June 16 and October 31, 2025, the City of Barrie is conducting a larviciding program under the authority of the Local Medical Officer of Health to control larval mosquitoes to prevent their development into vectors of West Nile Virus. The pellet formulation of Altosid Methoprene Pellets Mosquito Growth Regulator PCP#21809, or the pouch formulation of Vectolex WSP Biological Larvicide PCP#28009 is placed into municipal-owned catch basins of storm drains within the boundaries of the city of Barrie. 

All larvicide will be applied by applicators, licensed by the Ministry of the Environment, Conservation and Parks, or their supervised technicians. Municipal-owned catch basins on private property (rear Lot Catch Basins) are treated upon request of the homeowner with Altosid XR Briquette PCP#27694. A consent form must be signed by the homeowner prior to treatment.

For additional details on the locations and dates of treatment please call 705-790-1122.

Learn more about West Nile Virus Prevention

Prior to the commencement of the larviciding program, the City cleans out all catch basins, which ensures they are free of sediment and water and the larvicide remains in place for the appropriate time period and is not be flushed out. Additionally, the contractor does not apply the larvicide during rain events and uses a calibrated dispensing tool to ensure there are no excess amounts of larvicide. These methods prevent the larvicide from being flushed out of the intended catch basins and into the waterway. 

About the Larvicide Treatments

Approximately 95% of larvicide treatments are applied to roadside catch basins, which are not heavily colonized by other invertebrates. These catch basins typically contain high levels of organic matter and pollutants such as oil, road salt, and heavy metals—conditions that significantly reduce larval biodiversity. However, mosquito larvae thrive in these environments, as they are well-adapted to tolerate pollution and face little competition from other species.

The remaining 5% of treatments target temporary stagnant water bodies that appear and disappear with rainfall. These sites usually persist for only 7 to 10 days and are rarely colonized by organisms other than mosquito larvae.

Additionally, the biological larvicide used in stagnant water bodies is specifically designed to target mosquitoes, as it acts on the alkaline pH of their gut—an adaptation mosquitoes use to digest blood.