Great Lakes Environmental Assessment and Mapping Project

Invasive Species



Scientists have identified the Great Lakes as the most invaded freshwater system on the planet. Presently, more than 180 nonindigenous species have been reported in the Great Lakes, some having profound impacts and causing significant environmental change.


What is an invasive species?

An invasive species is a plant or animal that is non-native to an ecosystem whose introduction is likely to cause economic, human, or environmental damage. Once established, an invasive species is extremely difficult to control.

  • The earliest Great Lakes invasions were the result of deliberate and accidental releases. Other early invasions occurred by the movement of exotic species into the Great Lakes through new waterway connections created by the buidling of canals.
  • The rate of introductions increased with increasing economic activity, especially since the opening of the St. Lawrence Seaway in 1959, which allowed ships from international ports access to the Great Lakes for the first time.
  • More than two-thirds of aquatic invasive species introductions occurring between 1959 and 2000 have been attributed to ballast water releases from transoceanic ships. Notorious invaders like the zebra mussel, quagga mussel, and round goby were all introduced via ballast water.
  • The majority of Great Lakes invaders are native to Eurasia.
  • Species from the Ponto-Caspian region (Black, Caspian, and Azov seas) have been especially successful in the Great Lakes.
  • Management efforts to limit the range expansion of invasive species that have become established in the Great Lakes are generally costly and rarely successful.


Mapping invasive species as Great Lakes stressors

The cumulative stress map incorporates data for five invasive species stressors and one predictor of invasion. These stressors are a subset of those identified as important Great Lakes threats by a team of experts during a workshop in 2011. Other species identified, but for which basinwide spatial data are not currently available, included:

  • Submergent aquatic plants (e.g., Eurasian milfoil)
  • Rusty crayfish
  • Certain zooplankters (spiny water flea (Bythotrephes longimanus) and  fish-hook water flea (Cercopagis pengoi))
  • Emerging fish diseases (e.g., VHS - viral hemolytic septicemia)