Impaired Waters Source Categories

Waters considered impaired tend to fall into one of several distinct groups based upon the type of impairment that they possess as well as the dominant source of the impairment. For example, below you will see a category for atmospheric dominated waters -- these are waters that are listed for contaminants that are present due to atmospheric deposition of mercury. Below are descriptions of the types of categories with associated impairments, pollutants and recommended monitoring. Within each category is a description of the strategy the Department may use in development and implementation of TMDLs.

Nonpoint source dominated
These waters comprise the majority of the impaired waters list (33 percent). These are waters in which impairments (degraded habitat, low dissolved oxygen levels, elevated temperature) are due to nonpoint source runoff including destruction of instream habitat from pollutants including sedimentation and excess phosphorus. Many of these waters are headwater segments or subwatershed areas. Others are large bodies of water at the downstream end of large drainage basins. Waters affected by urban stormwater tend to fall into this category.

Atmospheric deposition dominated
The next largest group are those waters listed due to atmospheric deposition of toxic substances, such as mercury (21 percent). This regional issue results in elevated concentrations of contaminants in the water column or sediment, which in turn bioaccumulates - or concentrates - in fish tissue. Specific fish consumption advisories are issued for those situations in which the concentrations in fish tissue are above those levels determined for safe fish consumption. Most of these waters are lakes and main stems of major rivers. Waters impaired by atmospheric deposition were identified using the state's fish consumption advisory list.

Point source and nonpoint source blend
Point and nonpoint source blended waters at 16 percent comprise the third largest group of listed waters. These are waters in which nonattainment of standards is affected by both point source contributions and nonpoint source runoff, and in which both may be contributing to the failure to achieve water quality standards. Listing a water affected by a point source does not imply that the source is not meeting all the requirements in its discharge permit, but simply indicates that additional analyses are needed to determine relative contributions by the sources and what additional requirement, if any, might be needed.

Contaminated sediment waters
Contaminated sediment dominated waters (17 percent of the listed waters) are those waters in which specific contaminatd sediment deposits are believed to provide the source of concentrated toxins to the water column and fish tissue. These sites are located statewide but many are found in Great Lakes Bays and Harbors. The state is working diligently to obtain federal and state funding to remediate these sources of contamination and thus eliminate these waters from the state's impaired waters list.

Waters (usually segments of waterbodies) in which the impairment is present primarily as a result of toxic or other substances in the sediments which may be affecting either the ecology or uses of the site or moving off-site and affecting other uses of the water at locations beyond the boundary of the contaminated sediment. Contaminated sediments frequently are associated with the bioaccumulation of contaminants in fish and wildlife, thereby resulting in consumption advisories or harm to wildlife populations. The list of contaminated sediment waters originates from a list which was developed cooperatively by the Department's Remediation and Redevelopment and Watershed Management programs.

Habitat/physical impaired
About 2 percent of the state's impaired waters list are due to habitat and physical modifications. These are waters in which the impairment is present primarily as a result of destruction of habitat for aquatic organisms due to flow obstructions or physical barriers to the movement of water where aquatic organism populations are impacted by alterations in the natural flow of water at a particular site. These waters are usually stream segments or may be impoundments. (Note: Habitat impairment caused by point or nonpoint sources are not included in this category.)

The Department is aware of concerns which exist regarding the impact of dams (including beaver dams and other impoundments), channelization, and other physical changes on water resources. However, the database for making consistent decisions regarding such impairments has not been fully developed to select sites for inclusion on this list. Waters listed under this category will be addressed in a variety of ways depending on the nature of the impairment and the program activities which are deemed best for the location; operations of dams which affect organism populations may be addressed through licensing of dams or other orders the Department may issue.

Point source dominated
Point source dominated waters comprise less than 1 percent of all listed impaired waters. Waters (usually waterbody segments rather than entire streams or rivers) in which the impairment due to a current discharge from an existing point source. The WPDES program is implemented to assure the attainment of standards at the time of permit issuance. Existing law and rules including the water quality standards and WPDES permit rules preclude the issuance of a permit if it will not attain water quality standards. TMDLs in this category may also be implemented through the development of wasteload allocations under the provisions of NR 212.

Other factors
Waters in this category primarily include large waters, involving basins, or multibasin areas, which may be impaired as a result of several different categories of impairment or there are uncertainties regarding the cause of impairment.

For questions and comments about the material contained in this site, contact: Carolyn Betz, Bureau of Watershed Management.