The Great Lakes are home to more than 300 invasive or non-native species,and manythreaten the health of the aquatic ecosystem,a new report says.

Many of these plants and animals are destructive and parasitic, according to the report issued Monday by Environment Canada and the U.S. Environmental Protection Agency.

"The entry of non-native species … in the Great Lakes —that's a huge concern, [especially] how they compete with our native species and, in some cases, may replace them or drive them out of certain habitats," Nancy Stadler-Salt of Environment Canada said Monday.

"And once they're here, they're probably next to impossible to eradicate — it's just learning how to control them."

Invasive species include the zebra mussel, first detected in 1980, which upsets the natural balance by competing with zooplankton for food and suffocating existing mussel populations. The round goby and the Asian carp are two particularly destructive species of fish that arrived in the Great Lakes in the 1990s.

Many invasive species hitch a ride in the ballast water used to provide stability to cargo ships. When the ship dumps its ballast water into foreign regions, it often releases a slew of organisms from its home port.

In May, a U.S. environmental group called Healing Our Waters-Great Lakes Coalition called for a moratorium on international shipping, saying the damage caused by invasive species tops $5 billion US annually.

TheEnvironment Canada-EPA jointreport did find some positive news, saying the Great Lakes continue to be a good source for treated drinking water, noting the levels of toxic chemicals in the water has declined.

But it also says changes in climate —including shorter winters, higher annual temperatures and extreme heat events, are likely to reduce ice cover on the lakes, forcing wildlife from their natural habitats.