AIS: What Are AIS?

What Are Aquatic Invasive Species? 

PictureZebra Mussels

Aquatic invasive species (ais) are non-native aquatic animals, plants, and organisms that are 1) present in an ecosystem beyond their native range and 2) whose introduction can cause, or is likely to cause, a negative impact to our environment, economy, recreational activities, and public health.

The term “invasive” refers to the most aggressive non-native species.
No, actually only a small percent of introduced species ever become invasive. However, it is nearly impossible to predict which species will become invasive. Some species are present for many years before they exhibit invasive characteristics. Many invasive species go through a “lag phase” in which their populations grow slowly until they reach a size large enough for the population to explode and/or become adapted to the local environment and become invasive.

In their native environments, species have natural predators, competitors, parasites, pathogens and other biological mechanisms to keep the species in check and create a balance. However, when a species is introduced to a new environment, the checks and balances from its native range are missing in its new environment.

Now free from the checks and balances from its native range, the introduced species can effectively change the biodiversity of its new environment to suit its needs.  As a result, the species can become aggressive, reproduce and spread rampantly, crowd out or replace native species, change food webs, reduce biodiversity, cause ecological havoc in many of our most sensitive habitats, harm fisheries, interfere with recreational activities, destroy crops, spread diseases, interfere with commercial industries, and cost billions of dollars annually to destroy. To makes matters worse, approximately 42% of Threatened or Endangered species are at risk due to invasive species.!

Unfortunately, human actions are the primary means of invasive species introductions. For more information, see HOW DID THEY GET HERE? AIS PATHWAYS


  • Outcompete and displace native species.
  • Affect ecosystem structures, provisions, and functions, resulting in a loss of biodiversity or unique habitats.
  • Cause a dramatic shifts in food web structures, species abundance, and trophic dynamics.
  • Harm fisheries and threaten recreational and commercial activities.
  • Alter gene pools through hybridization with native species.
  • Serve as vectors of diseases – host pathogens and parasites harmful to fish and other aquatic species.
  • Decrease the aesthetics of our environment and reduce property values.​
AIS are found in water and on land.  In fact, AIS can occur in just about every type of aquatic and semiaquatic habitat you can imagine, spanning the gamut from lakes, rivers, creeks, streams, and wetlands to shorelines, uplands, wet meadows, woodlands, ephemeral pools, fields, and roadside ditches – all of the native areas throughout the state.

Unfortunately, human actions are the primary means of invasive species introductions. To learn how AIS is transported from one infested waterbody to an uninfested waterbody, see HOW DID THEY GET HERE?

In Wisconsin, the Invasive Species Identification, Classification, and Control Rule (NR 40) classifies invasive species in Wisconsin as Prohibited or Restricted and regulates the transportation, possession, transfer, and introduction of those species. . This rule also establishes “Preventive Measures” to show actions we can take to slow the spread of invasive species. The Invasive Species Rule covers over 128 species and affects everyone in Wisconsin. 

Prohibited Invasive Species:

  • Not yet in the state or only in a few places 
  • Likely to survive and spread
  • Potential to cause significant environmental or economic harm or harm to human health
  • Eradication and prevention is feasible
  • Regulations: Cannot transport, possess, transfer or introduce without a permit. Control is required. DNR may order or conduct a control effort. 

Restricted Invasive Species:

  • Already widely established in the state
  • Causes significant environmental or economic harm or harm to human health
  • Complete eradication is unlikely
  • Regulations: Cannot transport, transfer or introduce without a permit. Possession is allowed except for fish or crayfish. Control is encouraged but not required.

Under the Invasive Species Rule, any viable part of the species is regulated. Certain exemptions do exist with these regulations. Please consult the DNR website or DNR staff for clarifications.