Big Rideau Lake Aquatic Invasive Species Watch

Prepared by: Brook Schryer, Aquatic Invasive Species Outreach Liaison, Ontario Federation of Anglers and Hunters

Invasive species are one of the greatest threats to the biodiversity of Ontario’s waters. An aquatic “invasive” is defined as a non-native fish, animal, or plant species that has been introduced into a new aquatic ecosystem and is having harmful consequences for natural resources and the economy, including human health. 

The Invading Species Awareness Program (ISAP) is delivered through a long-standing partnership between the Ministry of Natural Resources and Forestry (MNRF) and the Ontario Federation of Anglers and Hunters (OFAH). ISAP’s goals are to spread education and outreach to Ontario’s public on the threats of invasive species. ISAP is also committed to identifying and addressing how invasive species are introduced and tracking their spread in the province. 

 There are a number of aquatic invasive species that have been reported and confirmed in Big Rideau Lake (for a full list, check out; however, this article is going to introduce three species to you that have either been identified in, or are a threat to Big Rideau Lake, these include: round goby (not present at this time), rusty crayfish (present in Big Rideau Lake), and European Chestnut (confirmed in the same watershed as Big Rideau Lake). 

Round Goby

 Round goby are a small, bottom dwelling fish native to Eastern Europe that were first reported in the St. Clair River in 1990. Though this species was most likely introduced via ballast water from ships entering the Great Lakes, it has since spread across southern Ontario through natural expansion and their illegal use as bait, which includes the dumping of bait buckets. This invasive fish is extremely disruptive through its ability to reproduce up to three times per season and feeds aggressively on zooplankton, invertebrates, and even our native fishes’ young and eggs. If caught while angling, be sure to take a photograph, report, then euthanize and place the round goby in the nearest garbage. It is also important to note that it is not encouraged that Round Gobies be fed to birds as they are linked to the transfer of Botulism Type-E. 

In order to ensure you are euthanizing the invasive round goby and not a native look-a-like (e.g. slimy sculpin), look for the prominent black dot on the first dorsal fin. Besides that, look for the fused scallop-shaped pelvic fin (just under the belly behind the head) which is what they use to keep themselves on the bottom of the infested waters. Finally, they are relatively small, ranging between 4-15cm in length with frog-like eyes and a blunted snout. 

Rusty Crayfish  

Rusty crayfish are an aggressive invasive species native to the Ohio River Basin. Rusty crayfish were first discovered in Ontario in the Kawartha Lakes in the 1960s and have since spread to many inland waterbodies in southern and northern Ontario. Rusty crayfish compete directly with our smaller, native crayfish species and will even crossbreed with them, creating a hybrid crayfish.  

Their diet consists of large amounts of plant life, negatively impacting important hunting and spawning habitat for our native species. These crayfish are capable of growing upwards of 13cm in length and a single female can carry up to 200 eggs under her tail. With this in mind, no rusty crayfish, dead or alive, should ever be transported across land and should only be used for bait in the waterbody where it was caught. 

If you suspect you have encountered a rusty crayfish, which has been reported in Big Rideau Lake, look for the distinct rusty patches on its carapace, the black bands on the tips of its claws, and an obvious gap in its claws when shut. 

European Water Chestnut  

Though European water chestnut is not in the immediate vicinity of Big Rideau Lake, it is in the watershed in the Rideau River within Ottawa’s city limits. This floating invasive aquatic plant was first introduced to North America from Europe, Asia, and Africa in the late 1800's. Currently, it is found in Quebec, the tributaries of the Niagara River, and Lake Ontario near Wolfe Island. 

European water chestnut poses a problem since it tends to create large monocultures that mat the surface of the water, which decreases native plant biodiversity and makes recreational activities like swimming, angling, and boating almost impossible in infested areas. In addition, the plant produces a ‘woody’ seed that has sharp spikes which sink to the bottom of the waterbody and can stay viable for over 10 years. These seeds also pose a health risk to swimmers that may accidentally step on the sharp seed. 

If you think you have encountered European water chestnut, look for the floating, leathery bright green leaves that form around a centre up to about 30cm in diameter. It also produces flowers that are 8mm long, white, and have 4 petals. 

If you suspect you have encountered a round goby, rusty crayfish, European water chestnut, or any other invasive species while on Big Rideau Lake, take a picture, and report it to the Invading Species Hotline at 1-800-563-7711. Alternatively, if you would prefer to report online, send an email to or make an account on and submit a report!  

Lyse PrendergastComment