The 2012 Great Lakes Water Quality Agreement states that “the Waters of the Great Lakes should be free from the introduction and spread of aquatic invasive species and free from the introduction and spread of terrestrial invasive species that adversely impact the quality of the Waters of the Great Lakes.”
Prevention (Rate of New Aquatic Nonindigenous Species Establishment)
Impacts of Aquatic Invasive Species
Assessment highlights
The assessment for this indicator is based on two components: Prevention, measured as Rate of New Aquatic Nonindigenous Species (also known as non-native species) Establishment into the Great Lakes (assessed as Good with a 10-year trend of No Trend), and Impacts of Aquatic Invasive Species (AIS) (assessed as Poor with a 10-year trend of No Trend). These assessments highlight that there has been success in preventing the establishment of aquatic non-native species (species that are not native to the Great Lakes basin that may or may not have known negative environmental and/or socioeconomic impacts); however, some established AIS (species that have known negative environmental and/or socioeconomic impacts) continue to expand their ranges. As of 2023, 190 aquatic non-native species have been reported as established in the Great Lakes, of which 78 are considered invasive.
Historically, ballast water from transoceanic ships served as the primary vector for the introduction of non-native species into the Great Lakes. There has been success in reducing establishments from outside of the Great Lakes in recent decades. This reduction is largely due to the implementation of regulations on ballast water and mandatory mid-ocean flushing of ballast tanks of all transoceanic ships as well as implementation of inspection programs to confirm that these ships are managing ballast water. No new aquatic non-native species suspected to have been introduced through ballast water have become established in the Great Lakes since 2006. Further, regulations regarding treatment systems for ballast water introduced by the Canadian government in 2021 (phasing in by 2030) aim to reduce the spread of aquatic non-native species within the Great Lakes basin.
From 2014 to 2023, four new non-native species of Zooplankton, all of which were suspected to be introduced through means other than ballast water, established overwintering and reproducing populations in the Great Lakes (Thermocyclops crassus, Mesocyclops pehpeiensis, Salmincola californiensis, and Diaphanosoma fluviatile). Despite the establishment of these four species, there has been a significant slowdown in establishments of aquatic non-native species compared with the rate from two decades ago, prior to the implementation of ballast regulations.
Preventing the establishment and spread of invasive species is essential for protecting Great Lakes native species and habitats. AIS can spread within and between the lakes, including by hitching rides on boats, trailers, and gear used by anglers, boaters, and other recreationists.
Since 1950, the cumulative impact of AIS on the Great Lakes has more than doubled. This cumulative impact takes into account the increase in the number of AIS, their spread between lake basins, and the magnitude and range of their individual impacts.
The Sea Lamprey is a prominent AIS and a lethal parasite of many Great Lakes fish species, such as Lake Trout. Annual control activities in the Great Lakes have successfully suppressed Sea Lamprey populations by approximately 90% since pre-control efforts. However, travel restrictions and unfavorable weather conditions in 2020-2021 led to decreased Sea Lamprey control activities, resulting in increases in their recent 3-year average populations, which now exceed target levels in four of the five Great Lakes.
Dreissenid Mussels (Zebra and Quagga Mussels) are AIS that have significantly impacted the Great Lakes ecosystem. They alter nutrient cycling, increase water clarity, and modify Phytoplankton and Zooplankton communities. Quagga Mussels have largely displaced Zebra Mussels in the Great Lakes due to a combination of factors including their ability to colonize deeper, softer substrates, survive in environments with lower food availability, and tolerate colder water temperatures. These advantages allow Quagga Mussels to outcompete Zebra Mussels in a wider range of habitats within the Great Lakes ecosystem.
In lakes Michigan, Huron and Ontario, Dreissenid Mussel populations in the shallow and mid-depth regions (less than 90 meters) are stable or declining. In areas deeper than 90 meters in Lake Michigan, populations continue to increase. In Lake Huron, densities increased to an all-time high in 2017 but have declined since then. In Lake Erie, overall lakewide Dreissenid Mussel densities are approximately four times lower than the peak levels of the 1990s; however, decreases in density vary between the western, central, and eastern basins of the lake. Lake Superior Dreissenid Mussel populations remain low, with some recent localized occurrences in coastal areas.
Terrestrial invasive species such as Emerald Ash Borer, Mute Swan, and Garlic Mustard are widely distributed in the Great Lakes basin and have detrimental impacts on the ecosystem. Community-based science data collection efforts are valuable sources of information for terrestrial invasive species distribution and are used to inform the sub-indicator.
Sub-indicators supporting the Invasive Species assessment
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Rate of New Aquatic Nonindigenous Species Establishment into the Great Lakes Basin | Great Lakes Basin assessment is Good & No Trend | ||||
Impacts of Aquatic Invasive Species | Poor & No Trend | Poor & No Trend | Poor & No Trend | Poor & Deteriorating | Poor & No Trend |
Sub-indicators provided for background information, but not included in the Invasive Species assessment
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Rate of New Aquatic Nonindigenous Species Establishment into Each Lake Basin | Poor & Improving | Fair & No Trend | Poor & Improving | Fair & Improving | Poor & No Trend |
Sea Lamprey | Poor & No Trend | Good & No Trend | Poor & No Trend | Fair & Improving | Poor & Deteriorating |
Dreissenid Mussels | Good & Unchanging | Poor & Deteriorating | Poor & No Trend | Fair & No Trend | Poor & Deteriorating |
Terrestrial Invasive Species | The methodology used to assess this sub-indicator is being updated. This sub-indicator is currently assessed as Undetermined. | ||||
The overall assessment for the Rate of New Aquatic Nonindigenous Species Establishment in the Great Lakes sub-indicator is solely based on new establishments in the Great Lakes; the lake-to-lake spread component provides additional information about the movement of non-native species between the lakes. Sea Lamprey and Dreissenid Mussels are among the species already included in the Rate and Impacts sub-indicator assessments. The Sea Lamprey, Dreissenid Mussels, and Terrestrial Invasive Species sub-indicator reports provide more detailed, supplementary information.
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