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Learn About Invasive Species

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Aquatic Plants


Invasive aquatic plants pose serious threats to all water bodies; they damage the ecosystem, cost money, and reduce water quality for recreational use. Aquatic plant invaders form dense mats of vegetation that block sun light and decrease any native plant from growing (which in turn decreases native wildlife which rely on the native plants). Once the invading plants begin to die the decomposers consume the oxygen in the water, creating an inhospitable environment for native aquatic species.  These mats also pose a serious problem for boaters and others using the water for recreation. Boat propellers can very easily get stuck in the plant’s stalks and the thick weeds make it impossible to swim in invaded areas. Because they are in water bodies, aquatic plants are hard to remove effectively. Chemicals can spread quickly, so herbicides are difficult to use in invasive aquatic situations. To prevent the spread and establishment of invasive aquatic plants all recreational equipment must be properly cleaned after use, and boats should never be driven through invasive plants as they can be quickly spread through stem fragmentation.


Water Soldier

Water soldier is a perennial aquatic plant that has long thin serrated leaves that grow in a rosette formation (similar to the top of a pineapple). The dense mats that form crowd out other vegetation and alter water chemistry causing decreased biodiversity of native aquatic species. Water soldier can be submerged up to 5 meters but floats to the surface in summer. This poses a threat to summer recreational activities such as fishing, boating, and swimming. Boat motors can break up plants allowing them to spread and invade new areas. Learn to identify water soldier, avoid spreading it by slowing down when boating through areas it is present and by cleaning all your recreational equipment after use. The only population in North America is in the Trent River and there are many efforts in place to control and prevents its spread.

Fact Sheet

Eurasian Water Milfoil

Eurasian Water Milfoil is a perennial aquatic plant that grows under the water surface. Its leaves are feather-like with 12 or more thin segments (native milfoil has 11 or fewer leaf segments). Normally submerged under one to three meters of water, it blooms small reddish flowers that rise above the water in July and August. Eurasian water milfoil grows in thick dense mats that crowds out native species, reducing biodiversity, and deoxygenate water when decomposing, killing other aquatic species. It can also cause damage to boat motors, negatively impacts fishing and swimming, and increases suitable mosquito habitat. Eurasian water milfoil is spread through fragmentation of plants and the release of aquarium plants and pets. To prevent its spread avoid boating through invaded areas, wash all recreational equipment, and never release or compost unwanted aquarium vegetation.

Fact Sheet

European Water Chestnut

European water chestnut is an aquatic plant with a hard stem that can reach up to three to five meters. The leaves sit above the water, spread out in a circular pattern, and are triangular with serrated edges. In June European water chestnut blooms small white flowers with four petals. The dense floating leaves shade out the water below, killing native vegetation and subsequently reducing water oxygen levels. The plants also get tangled in boat motors and make swimming almost impossible. European water chestnut seeds are 3-4 cm wide and have sharp barbed spines which are very painful to step on, making swimming or walking in invaded areas dangerous. Try to avoid boating or recreating in areas that contain European Water Chestnut and always wash equipment after being in the water. Do not plant invasive species in ponds and never release unwanted aquarium plants.

Fact Sheet

European Frog-bit

European Frog-bit resembles native water lilies, but it has smaller lease (2-5 cm) and the small (2 cm) white flower has three petals and a yellow center. It can be free floating or root in shallow water. European Frog-bit leaves crowd out the surface of lakes preventing any native plants from growing, and as these large mats of vegetation die they deoxygenate the water which harms native fish and aquatic species. New plants can grow from stem fragments which makes it very easily spread by boat disturbance. To prevent the spread of European frog-bit avoid operating motorized watercrafts through or near patches, thoroughly clean all vegetation and mud from your water equipment, and never plant it in water gardens.

Fact Sheet


Although hydrilla has not been reported in Canada, it is found in many neighbouring states. With the shared waterways between Canada and the U.S. it is very important to control the spread of all aquatic species. Hydrilla grows underwater with rooted stem reaching up to 7.5 metres high, with rows of three to eight tiny (1-2 cm) green leaves arranged in circles around the stem. The leaves have serrated edges and prickly hairs on the underside. Hydrilla can dramatically degrade water quality causing a decrease in native species by blocking sunlight, decreasing oxygen levels, raising pH levels, and increasing water temperature. It also makes swimming, boating and fishing very difficult and decreases water flow which can create mosquito breeding grounds. Hydrilla is very easily spread by fragments of the plant, always take extreme care when boating around affected areas and wash your boat and recreation equipment thoroughly after use.


Fanwort is a submerged plant in lakes in rivers that has pairs of finely divided, fan shaped leaves that grow on opposite sides of the stem, giving the plant a feather like appearance. It can also have small oblong leaves that float on the surface. Fanwort blooms very small (0.6-1.5 cm) flowers in summer and can be white, yellow, purple or pink. Because fanwort is so fast growing it quickly blocks out native plants which in turn disrupts the native fish community, and it can clog drainage systems. Thick stands can make it impossible to swim, fish, or boat. Avoid operating recreation vehicle around fanwort patches, boat propellers can easily break the plants which can lead to new populations establishing. Do not use fanwort in aquariums or water gardens.

Fact Sheet