Many aquatic invasive species (also known as exotic species) are a persistent problem in U.S. coastal and inland waters. Invasive species pose several dangers to aquatic ecosystems, including outcompeting native species, damaging habitat, and altering the chemical and physical aquatic
environment. This can disrupt the balance of the local ecosystem, harming fish and shellfish stocks, degrading water quality, and causing plant overgrowth that affects boating and swimming. Threatened or Endangered Species may be especially vulnerable to the impacts of introduced species because
these populations are already under stress. Questions have arisen in various contexts as to the status of invasive species for purposes of the 303(d) Listing and Total Maximum Daily Load (TMDL) Program. In the past 12 years of listing cycles, the U.S. Environmental Protection Agency (USEPA)
has approved a small number of waters listed for invasive species in at least 16 states and has disapproved lists for failure to include waters impaired by invasive species in 2 states. A few states have approved TMDLs for invasive species. As a result of a 2006 court ruling related to invasive
species in ship ballast water, thousands of non-recreational vessel owners and operators who were exempt from Clean Water Act (CWA) requirements for the last 35 years must seek coverage under a NPDES permit. Most recently, six states and two USEPA Regions received comments from the National
Wildlife Federation (NWF) on their 2008 lists regarding the presence of invasive species, and NWF requested that states revise their 303(d) lists to include waters impaired or threatened by invasive species. The different approaches taken by the states may reflect the fact that USEPA has
not determined whether invasive species are pollutants within the definition of CWA Section 502(6) and has not provided specific guidance to the states on how to address waters that may be impaired by invasives. In addition, some states may not have appropriate methodologies for assessing
invasive species impairments. This paper summarizes some actions that several states have taken related to invasive species in their 303(d) programs; discusses how a few states have dealt with invasives in their assessment methodologies, water quality standards, and approved TMDLs; and provides
information that could be used to inform USEPA's actions on this issue in the future.
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