ASSESSMENT

ASSESSMENT METHODOLOGY A. Consolidated Assessment Listing Methodology (CALM) All data used to make formal assessments of the quality of the state’s waters, regardless of its source, are evaluated in keeping with the requirements and guidelines in the state’s Mississippi CALM [Consolidated Assessment Listing Methodology] for 2026, [CALM] (MDEQ, 2026). The 2026 CALM can be found online at: https://www.mdeq.ms.gov/water/field-services/water-quality-assessment/ Monitoring data and information that may be considered when assessing state waters could include chemical, physical, bacteriological, toxicological, and/or biological (e.g., macroinvertebrate, fish, and algal community measurements) data. In addition to using MDEQ-generated data, MDEQ solicits and considers all readily available data and information within the assessment window collected by other Federal, State, local agencies/organizations, and the public. Data generated by MDEQ, other agencies, and individuals should be of the quality necessary to make credible and realistic assessment decisions on the condition of the state’s waters. Whenever possible, data needs to be of the highest quality and developed using sampling and analytical protocols and standard operating procedures recognized by state and EPA quality assurance program plans. This data solicitation effort is facilitated through MDEQ’s Basin Management Approach. B. Designated Uses The water quality assessment process begins with the collection and compilation of the available data followed by the analysis of water quality data and information for the purpose of determining the quality of the state’s surface water resources. Surface waters in Mississippi are used for a number of purposes including drinking water supply, shellfish harvesting, recreation, fishing, and aquatic life use support (ALUS). Water bodies are designated and assigned various use classifications by MDEQ in the state’s Water Quality Standards (11 Miss. Admin. Code Pt. 6, Ch. 2) {WQS}. This designation is made based on the use(s) of the water body as identified by the public and other entities. The use classifications and associated USEPA designated uses for water quality assessment purposes recognized by the State of Mississippi are given in Table 1. Table 1 Water Body Classification Water Body Classification USEPA Associated Designated Use Public Water Supply Drinking Water Supply Recreation Contact Recreation Fish and Wildlife Aquatic Life Use, Fish Consumption, Secondary Contact Recreation Shellfish Harvesting Shellfish Consumption C. Water Quality Standards Most of Mississippi’s waters are classified as Fish and Wildlife. For each of the water body classifications listed above, there are various water quality criteria that apply to those water body uses. These standards are used in the assessment process. A water body (part or all of a stream, river, lake, estuary or coastline) should support one or more of these uses. Mississippi’s WQS specify the appropriate levels for which various water quality parameters or indicators support a water body’s designated use(s). Each use assessed for a water body is determined to be either “Attaining” or “Not Attaining” in accordance with the applicable water quality standards and EPA guidelines for assessments pursuant to §305(b). For the 2026 assessments, all monitoring data were collected prior to the approval of the current Water Quality Criteria for Intrastate, Interstate, and Coastal Waters. The applicable criteria was approved in 2021. Mississippi's WQS may be found here: https://www.mdeq.ms.gov/water/surface-water/watershed-management/water- quality-standards/ D. Assessment Categories After assessing attainment status of the water body’s designated use(s), each water body is assigned to an assessment unit that defines the length of the reach assessed and is placed into one of five assessment categories as per EPA guidance. These categories are summarized in Table 2. Table 2 Assessment Categories Assessment Categories Definitions of Categories Category 1 All uses associated with the Assessment Unit have a use attainment status of “Fully Supporting” Category 2 All uses associated with the Assessment Unit that have been assessed are “Fully Supporting” but there is insufficient data to determine if remaining designated uses are met Category 3 Insufficient data to determine whether any designated uses are met Category 4 More specific categories of 4A, 4B, and 4C are required 4A TMDL has been completed 4B Other required control measures will result in attainment of WQS 4C Impairment or threat not caused by a pollutant Category 5 Available data indicate that at least one designated use is not being supported and a TMDL is needed 5R Available data indicate that at least one designated use is not being supported, but an alternative restoration approach is being implement rather than development of a TMDL. The §303(d) list includes streams that are impaired that do not have completed Total Maximum Daily Loads (TMDLs). Once the TMDL is completed, but prior to the stream being restored, MDEQ modifies the assessment category of the stream. An impaired stream without a TMDL is assessed in category 5. A stream with a TMDL, but still impaired, is assessed in category 4A. The §303(d) lists all of the category 5 waters. Completed TMDLs may be found on the TMDL website at: https://opcgis.deq.state.ms.us/tmdls For a listing of all assessed waters and their assigned category, please see the §305(b) Water Quality Assessment Report listed below: https://www.mdeq.ms.gov/water/field-services/water-quality-assessment/ E. Monitoring Data Assessments for 2026 are based on current site-specific monitoring data believed to accurately portray existing water quality conditions. A water body is considered monitored if sufficient (in quantity, quality, and frequency) physical, chemical, biological, bacteriological, and/or fish tissue data were collected and assessed on the water body data from January 1, 2018 to December 31, 2025. Physical and chemical data include such parameters as pH, temperature, dissolved oxygen, toxicants, turbidity, total dissolved solids (TDS), and specific conductance. Biological data include the community structure of aquatic insects, other macroinvertebrates, fish, and/or algae. Bacteriological data include water column surveys for fecal coliform bacteria, E coli, or enterococci bacteria. Fish tissue data include the analyses of fish flesh for the presence of toxic organic chemicals and metals. The length of record of the data, the quality of the data, and the frequency at which the data are collected were considered in making use attainment decisions. For 2026, MDEQ considered all known and readily available information on the quality of the state's waters in conjunction with the rotating basin approach and MDEQ’s §305(b) assessment program. However, only data that allowed for the accurate interpretation of the state’s water quality standards or provided compelling evidence were used for §303(d) listing decisions.