TORONTO -- As many Canadians head out to enjoy nature this summer, a conservation group is encouraging them not to take invasive species with them.

The Nature Conservancy of Canada says activities such as camping, hiking, biking, fishing, boating, horseback riding and driving ATVs can unintentionally spread invasive species into rivers, streams and forests.

The group has released a list of the top 10 invasive species spread through summer recreational activities.

Conservation biologist Dan Kraus says the list contains some familiar species and others that may be surprising -- such as cats, which can kill birds and other wildlife of conservation concern.

The emerald ash borer beetle is spread by moving firewood, the spotted knapweed plant can be spread through hiking and camping, and the Eurasian milfoil is spread by boating.

Kraus says many invasive species have few natural predators to control them.

He says once they get into ecosystems, they're often able to spread and out-compete native plants and animals for space, water, food and other resources.

"People may unknowingly be contributing to the spread of invasive species when they are enjoying the outdoors through their recreational activities," Kraus said. "That's why it's important to share information so that people can minimize the spread of invasive species to new areas in Canada."

The Nature Conservancy of Canada is the country's leading not-for-profit, private land conservation organization.

Since 1962, the NCC and its partners have helped to protect more than 1.1 million hectares across the country.

 A list of the top 10 invasive species spread through summer activities in Canada

Spotted knapweed
This aggressive invasive plant invades prairies, meadows and open woods. It can take over these habitats and reduce the number and diversity of native plants and animals. Each plant produces thousands of seeds that can be spread when they adhere to ATVs, horses, bikes, hiking boots and camping equipment.
Where it's found: Yukon, British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick and Nova Scotia.

Garlic mustard
This biennial plant is rapidly spreading across Canada, into forests and woodlands. It can form dense stands that exclude native plants, and can impact forest regeneration. Garlic mustard can be spread when the small seeds adhere to boots and clothing.
Where it's found: British Columbia, Alberta, Ontario, Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador

Eurasian milfoil
Known as the "zombie plant," this aquatic weed grows quickly in the spring, forming a thick mass of tangled stems under water. These stems get caught in boat propellers and rudders and reduce native aquatic plants and impact fish habitat. It is primarily spread when boats are moved by trailer between lakes.
Where it's found: British Columbia, Manitoba, Ontario, Quebec, New Brunswick and Prince Edward Island

Round goby
This small, bottom-dwelling invasive fish was found in the Great Lakes in 1990 and is spreading. It reduces native fish populations by eating the eggs and young of species such as lake trout and smallmouth bass. Round goby can be spread when it's used as bait, or when released upstream from dams and waterfalls.
Where it's found: Great Lakes basin

Zebra and quagga mussels
These small freshwater mussels have been spreading across North America. They can completely cover the bottom of lakes, impacting fishes, native mussels and water quality. They are spread when they attach to boat hulls, trailers and motors that are moved between lakes.
Where it's found: Ontario, Manitoba and Quebec

Emerald ash borer
This non-native invasive beetle has decimated tens of millions of ash trees and continues to spread rapidly. It can quickly kill large areas of ash trees, affecting forests, areas along streams, and rivers and urban forests. It has spread to some areas through people moving firewood that has been cut from infected ash trees.
Where it's found: Manitoba, Ontario, Quebec and New Brunswick

Spiny waterflea
This small freshwater crustacean feeds on zooplankton in lakes. Spiny waterflea can alter the food chain and affect native fish populations. Large numbers of spiny waterfleas form a jelly-like mass that clogs fishing gear and other equipment. It is spread by water from infected boats or when bait buckets are moved between lakes.
Where it's found: Ontario and Manitoba

European and Asian earthworms
Many people are surprised to hear that most of the earthworms they encounter are non-native and invasive, including the "night crawler" often found in gardens and used for bait. Invasive earthworms damage forests, as they change the soil chemistry and structure. Earthworms can be introduced to forests by anglers dumping their leftover bait on land or in the water, and vehicles can transport earthworms or cocoons in their tire treads.
Where it's found: Throughout much of southern Canada

Whirling fish disease
This infectious invasive parasite affects salmon and trout. First found in Canada in 2016 in Alberta, this disease invades the fish's cartilage and impairs its nervous system, which causes it to swim in a whirling pattern. It can be spread by moving infected fishes, bait or boats between lakes and rivers.
Where it's found: Alberta

Domestic cats
Domestic cats can have a significant affect on populations of migratory birds, reptiles and small mammals, and are considered one of the world's 100 most invasive species. Cats that are brought to cottages and camps can kill birds and other wildlife and should be kept indoors, or on a leash outside.
Where it's found: Throughout Canada