NR 102.55(1)(1) General. This section establishes narrative biological assessment thresholds that characterize the biological community condition and that are used to measure attainment of aquatic life designated uses specified in s. NR 102.04 (3) for surface waters. This section also establishes methods for evaluating attainment of narrative assessment thresholds.

NR 102.55(2)(a)(a) The aquatic life uses under s. NR 102.04 (3), except for those specified in s. NR 102.04 (3) (d) to (e), shall be considered suitable for the protection and propagation of a balanced aquatic life community. Those uses are intended to support the growth, development, reproduction, and life cycle of the aquatic life communities for their designated aquatic life use categories, although such waters may exhibit moderate changes in aquatic life community structure due to loss of some rare native taxa or shifts in relative abundance. In determining attainment of a waterbody’s designated uses, the department may compare its biological quality to the range of quality found in similar waterbodies under natural conditions. A waterbody with distinct natural characteristics that result in an aquatic life community different from or less diverse than other waters in the same use category may be considered attaining its aquatic life use if those differences are clearly related to natural characteristics.

NR 102.55(2)(b)(b) A surface water that does not support a balanced aquatic life community as designated under s. NR 102.04 (3) (d) to (e) shall support its highest attainable use given its habitat and potential.

NR 102.55(2)(c)(c) A surface water shall maintain at least the highest biological condition it has achieved since 1975.

NR 102.55 NoteNote: Paragraphs (b) and (c) reflect federal requirements under 40 CFR s. 131.10 (g), pertaining to highest attainable uses, and 40 CFR s. 131.3 (e), specifying November 28, 1975 as the benchmark date from which to determine “existing uses” for aquatic life.

NR 102.55 NoteNote: Examples of waterbodies with distinct natural characteristics are wetland-dominated streams, naturally acidic bog lakes, and ephemeral streams with only small areas of short-term refugia. Biological condition assessments should not be conducted during periods when there is insufficient water due to natural conditions to support aquatic life.

NR 102.55(3)(3) Assessment methods for narrative biological thresholds. Biological assessments for determining attainment of designated uses may be conducted in accordance with the assessment protocols specified in s. NR 102.52 and may include any of the following:

NR 102.55(3)(a)(a) Biological community assessments. To conduct biological community assessments, the department shall use documented methods that have undergone technical review and produce consistent, objective, and repeatable results that account for methodological uncertainty and natural environmental variability. Such methods include indices of biological integrity or similar tools calculated from measured attributes of resident fish, aquatic invertebrates, aquatic plants, or other aquatic communities. Such indices or tools may include measures of species composition, diversity, and abundance; feeding and reproduction characteristics; condition of individual organisms; or other scientifically objective, credible, and supportable factors. Historic records of native species may also be used to assess whether a waterbody exhibits loss of native species.

NR 102.55(3)(b)(b) Biological integrity trends. All surface waters shall maintain existing biological integrity, such that no waterbody or portion thereof shall experience a significant declining trend since 1975 using indicators under par. (a) or other indicators of biological condition, as demonstrated through scientifically-based documentation.

NR 102.55 NoteNote: An example of methods the department uses for assessing biological health of surface waters are those found in the department’s guidance for waterbody assessments, “Wisconsin Consolidated Assessment and Listing Methodology,” or WisCALM. Protocols for assessing attainment of biological assessment thresholds using metrics such as fish or macroinvertebrate indices of biotic integrity or the macrophyte assessment of condition are contained in, or referenced in, WisCALM. WisCALM is available on the department’s surface water assessment website at https://dnr.wi.gov/topic/SurfaceWater/assessments.html and is updated every 2 years with public input.

NR 102.56NR 102.56 Numeric biological assessment thresholds for lakes, reservoirs and impounded flowing waters. This section contains numeric biological assessment thresholds for evaluating the biological condition of lakes, reservoirs, and impounded flowing waters and determining whether applicable designated uses are being attained. Numeric biological assessment thresholds used to assess attainment of designated uses include all of the following:

NR 102.56(1)(a)(a) Chlorophyll a.

NR 102.56(1)(a)2.2. ‘Assessment methods.’ Data requirements for chlorophyll a are the same as those specified for phosphorus in s. NR 102.07 (1) (a), except that the sampling period for chlorophyll a is July 15 to September 15. To determine attainment of the chlorophyll a threshold under subd. 1., the department shall compare the waterbody’s mean suspended chlorophyll a concentration during the sampling period to the threshold, using the confidence interval approach described under s. NR 102.52 (2) (b) to (c) to determine if additional samples are needed.

NR 102.56(1)(b)(b) Aquatic plants.

NR 102.56(1)(b)1.1. ‘Assessment thresholds.’ Thresholds for evaluating the general health of an aquatic plant community in a lake or reservoir to determine whether its aquatic life use is attained are shown in Table 8. Thresholds used in the macrophyte assessment of condition indicate the acceptable percentage of a lake or reservoir’s vegetated area supporting species that are in each of three tolerance categories. The tolerance categories specify whether a plant species is sensitive to, moderately tolerant of, or tolerant of disturbance.

1In Table 8, northern lakes are those north of 44.84707°N latitude, and southern lakes are those south of that latitude. These thresholds do not apply to the Great Lakes or lakes less than 5 acres in surface area.

NR 102.56(1)(b)2.2. ‘Assessment methods.’ The percentage of a lake or reservoir’s vegetated area supporting each tolerance category shall be determined using department-approved protocols for assessing macrophyte condition. The sampling period for southern lakes is June 15 to September 15, and for northern lakes is July 1 to August 31 unless the department determines that an extension from June 15 to September 15 is appropriate during warmer than average years. The department shall consider the threshold attained if the most recent plant survey conducted within the past 10 years, or other more representative survey, attains the applicable threshold in Table 8.