Regulatory Information

Chemical Control of Aquatic Nuisances in and/or Near Surface Water


A permit is required when pesticides are used in a waterbody or within 50 metres of a waterbody to control aquatic nuisances.

All freshwater systems naturally evolve from relatively barren infertile (oligotrophic) waters to productive (eutrophic) systems supporting a wide diversity of organisms.

Human development around surface waters accelerates the evolution toward the mature productive stage and when unchecked, can lead to an unhealthy, over productive (hypereutrophic) level.

Most aquatic plants that are considered nuisances are a result of excess nutrients and occur in and around surface waters within two biologic zones:

  • the riparian or shoreline zone acts as a filter, removing nutrients from runoff prior to it entering the water body. Plants in this zone slow runoff thereby allowing water to soak in and replenish groundwater and they reduce erosion by anchoring soil in place; and
  • the littoral zone is the shallow water around the shore of lakes in which there is rooted vegetation. This zone also removes nutrients entering the system from runoff and the density of the growth can sometimes be used as an indicator of the amount of nutrients present. The use of aquatic vegetation (macrophytes) to filter water has been recognized and is being engineered into sewage and industrial treatment systems. The littoral zone is also the main habitat for tiny animals (zooplankton) and minnows, which in turn are the food source for game fish such as pike and walleye.


Certain aquatic plants and animals can be called "aquatic nuisances" when they become present in sufficient numbers to pose problems for people or animals using a water body or its surrounding environment. Aquatic ecosystems represent a delicate balance of many factors and the proliferation of certain aquatic plants and animals occur when the system becomes imbalanced.

This can occur naturally (e.g. mosquito outbreaks can result from wet or rainy weather), or be induced by man (e.g. excessive plant growth due to nutrients or pollutants from septic systems, agricultural fertilizers, urban runoff, industrial byproducts, etc.). Population outbreaks of certain aquatic plants and animals are generally an attempt by the aquatic ecosystem to restore its natural balance (e.g. excessive plant growth to use up excessive nutrients).

If the element that is causing the upset is reduced, the system will return to a state of balance. However, if the factor(s) that is causing the upset is not reduced or stopped the system cannot return to its balanced state.

The most effective means of aquatic nuisance control is to prevent the aquatic ecosystem from becoming out of balance. If the aquatic ecosystem is already out of balance, the next most effective measure is to eradicate the element or factor that is causing the system to be out of balance.

There may be a delay in seeing the results of reducing a nutrient, as the system will take a while to use up accumulated amounts of the element out of balance. If neither of the above is possible then the next alternative, aside from learning to live with the nuisance, is to reduce the specific nuisance.

This measure will merely be treating the symptom, not the cause of the problem. Measures to control one type of aquatic plant or animal can have undesired effects on other aquatic or terrestrial species. It is very important that effective and environmentally responsible control of aquatic nuisances is done.

This is only achievable once one acquires knowledge of the chemical alternatives, their pros and cons, the aquatic ecosystem and the types of aquatic plants and animals that may need to be considered at a particular site.