Chapter NR 102

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) (2) Narrative biological 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 Note Note: 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 Note Note: 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 Note Note: 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 102.55 History History: CR 19-094: cr. Register September 2022 No. 801, eff. 10-1-22.

NR 102.56 NR 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) (1) Aquatic life use thresholds.

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

NR 102.56(1)(a)1. 1. ‘Assessment thresholds.’

NR 102.56(1)(a)1.a. a. A lake or reservoir other than a stratified two-story fishery lake is not attaining its aquatic life use if its arithmetic mean suspended chlorophyll a concentration exceeds 27 ug/L.

NR 102.56(1)(a)1.b. b. A two-story fishery lake is not attaining its aquatic life use if its arithmetic mean suspended chlorophyll a concentration exceeds 8 ug/L.

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 Note Note: The aquatic life chlorophyll a thresholds do not apply to streams, rivers, or impounded flowing waters, as they were established based on lake trophic status levels.

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.

Table 8

Aquatic plant community thresholds for
lakes and reservoirs

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.

NR 102.56 Note Note: Examples of department-approved sampling protocols include the “Recommended Baseline Monitoring of Aquatic Plants in Wisconsin,” available on the department’s website in the Electronic Guidance and Documents (EGAD) system at https://dnr.wi.gov/water/egadsearch.aspx. Examples of department-approved analysis protocols include the “Macrophyte Assessment of Condition – General” (MAC-Gen) for general condition assessments applicable to this section, and the “Macrophyte Assessment of Condition – Phosphorus” (MAC-P) for phosphorus-specific assessments under s. NR 102.60 (2) (c). Each MAC protocol contains the tolerance groups assigned to each species. MAC-Gen and MAC-P scores can be obtained by contacting the department at [e-mail] and submitting aquatic plant data collected and formatted according to department specifications. Computer programming script written in the R language to compute the MAC calculations can be obtained through the department’s Water Evaluation Section by contacting the department’s call center at 1-888-WDNRINFo (1-888-936-7463) or using options provided on its website at https://dnr.wi.gov/contact/.

NR 102.56(2) (2) Recreation use thresholds.

NR 102.56(2)(a) (a) Definition. In this section, “moderate algae level” means a chlorophyll a concentration of 20 ug/L or greater.

NR 102.56(2)(b) (b) Frequency of moderate algae levels. Thresholds in Table 9 shall be used when determining if a lake, reservoir, or impounded flowing water is attaining its recreational use.

Table 9

Algae thresholds for recreational use assessments

1 Terms used for waterbody types and subcategories are defined in s. NR 102.03.

2 Summer sampling period is July 15 to September 15.

NR 102.56 Note Note: Lakes and reservoirs are subcategorized based on both their stratification status (stratified vs. unstratified) and whether or not they have an outlet stream or river (drainage vs. seepage). To find a lake or reservoir’s subcategory, also known as its natural community, go to the department’s Surface Water Data Viewer online map at https://dnr.wi.gov/topic/surfacewater/swdv/ and turn on the layer for Surface Water: Lake Natural Communities. On the natural communities layer, unstratified is referred to as “shallow,” and stratified is referred to as “deep.” Headwater and lowland lakes are types of drainage lakes.

NR 102.56 Note Note: The U.S. EPA has set human health swimming advisory levels for microcystin and cylindrospermopsin that accurately reflect the latest scientific information on the potential human health effects from recreational exposure to these two cyanotoxins. The department recommends that local and tribal public health agencies use these swimming advisory levels for notification purposes in recreational waters to protect the public. More information can be found at
https://dnr.wisconsin.gov/topic/lakes/bluegreenalgae.

NR 102.56(2)(c) (c) 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 in all waterbody types is July 15 to September 15. To determine attainment of the threshold, the department shall determine a waterbody’s frequency of moderate algae levels during the chlorophyll a summer sampling period using the confidence interval for a percentile of a normal distribution, and use the approach described under s. NR 102.52 (2) (b) and (c) to compare that frequency to the applicable threshold in Table 9.

NR 102.56 Note Note: The statistical calculation for determining the frequency of moderate algae levels is contained in Wisconsin’s Consolidated Assessment and Listing Methodology (WisCALM) guidance document.

NR 102.56 History History: CR 19-094: cr. Register September 2022 No. 801, eff. 10-1-22.

NR 102.60 NR 102.60 Combined assessment procedure for phosphorus.

NR 102.60(1) (1) General.

NR 102.60(1)(a) (a) This section establishes a combined assessment approach for making total phosphorus attainment determinations for surface waters in cases specified in par. (b). This approach is designed to account for variability in how waterbodies respond to phosphorus. The combined approach evaluates a waterbody’s quality by considering the total phosphorus concentration in the surface water in conjunction with an evaluation of the phosphorus response indicators specified in subs. (2) to (4). The phosphorus response indicators characterize the condition or abundance of aquatic organisms that are responsive to total phosphorus to determine whether aquatic life and recreation uses are being met. Together, the total phosphorus criteria and response indicators may be used to determine whether the phosphorus water quality standards are attained or whether the waterbody should be listed as impaired for total phosphorus on the section 303 (d) list.

NR 102.60(1)(b) (b)

NR 102.60(1)(b)1. 1. If a waterbody’s calculated total phosphorus concentration exceeds its total phosphorus criterion using the assessment procedure under s. NR 102.07 and the waterbody’s calculated phosphorus concentration is within the combined assessment range shown in Table 10, the department may make the total phosphorus attainment or impairment determination using phosphorus response indicators specified in subs. (2) to (4) if sufficient biological data are available to conduct these assessments. In that case, the following decision protocols apply:

NR 102.60(1)(b)1.a. a. A waterbody that attains all of its applicable phosphorus response indicators under subs. (2) to (4) may be excluded from the section 303 (d) listing of waters impaired for phosphorus.

NR 102.60 Note Note: If a waterbody is not considered impaired using the combined approach, it may be a candidate for a less stringent phosphorus site-specific criterion under ch. NR 119. If a waterbody attains its phosphorus criterion but one or more phosphorus response indicators are not attained, it may be a candidate for a more stringent site-specific phosphorus criterion under ch. NR 119.

NR 102.60(1)(b)1.b. b. If a waterbody does not attain one or more of the applicable phosphorus response indicators in subs. (2) to (4) or if the department does not have sufficient data to evaluate all of the applicable response indicators, then the waterbody shall be considered impaired for total phosphorus and the department shall propose inclusion of the waterbody on the section 303 (d) list as not attaining its phosphorus criterion. As part of the public comment period for the section 303 (d) list, the department shall provide a list of waterbodies needing additional data to determine whether phosphorus response indicators are met. If sufficient phosphorus response indicator data becomes available in the future, the waterbody may be reassessed.

NR 102.60(1)(b)2. 2. If a waterbody’s calculated phosphorus concentration exceeds its total phosphorus criterion using the assessment procedure under s. NR 102.07 and the waterbody’s calculated phosphorus concentration also exceeds the upper limit of the combined assessment range shown in Table 10, then the waterbody shall be considered impaired for total phosphorus regardless of attainment of phosphorus response indicators, and the department shall propose to include the waterbody on the section 303 (d) list.

Table 10

Range for applying combined assessment for
total phosphorus1

1To determine whether a waterbody falls into the combined approach range, compare the lower confidence limit of the waterbody’s two-sided 80% confidence interval around the mean (for lakes/rivers) or median (for rivers/streams) total phosphorus concentration to the ranges in the table.

2 For streams and rivers the combined criteria range is between the applicable total phosphorus criterion and two times that criterion. For lakes, the range is between the applicable total phosphorus criterion and 1.5 times that criterion. If a waterbody has an approved site-specific phosphorus criteria, the combined criteria range for that waterbody shall be calculated using these multiplication factors.

NR 102.60(2) (2) Lake and reservoir phosphorus response indicators. A lake or reservoir 5 acres or greater for which the total phosphorus concentration is within the combined approach range specified in Table 10 shall be listed on the section 303 (d) list as impaired for phosphorus unless it attains all of the following phosphorus response indicators:

NR 102.60(2)(a) (a) Frequency of moderate algae levels. The biological assessment thresholds for frequency of moderate algae levels to attain recreation uses as specified in s. NR 102.56 (2).

NR 102.60(2)(b) (b) Chlorophyll a. The chlorophyll a biological assessment threshold to attain aquatic life uses as specified in s. NR 102.56 (1) (a).

NR 102.60(2)(c) (c) Aquatic plants. The aquatic plant phosphorus response indicator for aquatic life use in this paragraph. Thresholds for assessing macrophyte community response to phosphorus levels in a lake or reservoir are shown in Table 11. Thresholds indicate the acceptable percentage of a lake or reservoir’s vegetated area supporting species that are phosphorus-sensitive or phosphorus-tolerant. Non-attainment of a threshold indicates that an aquatic plant community is considered degraded by phosphorus concentrations in the surface water. Assessment methods are the same as those specified in s. NR 102.56 (1) (b) 2. except percentages are compared against thresholds in Table 11.

Table 11

Lake aquatic plant community phosphorus
response indicator

1 In Table 11, northern lakes are those north of 44.84707°N latitude, and southern lakes are those south of that latitude. This plant phosphorus response indicator does not apply to the Great Lakes or lakes less than 5 acres in surface area.

NR 102.60(2)(d) (d) Oxythermal layer thickness. The oxythermal layer thickness criteria specified in s. NR 102.04 (4) (am). This paragraph applies only to two-story fishery lakes.

NR 102.60(3) (3) River and impounded flowing waters phosphorus response indicator. A river listed in s. NR 102.06 (3) (a), or its impounded flowing waters, for which the total phosphorus concentration is within the combined approach range specified in Table 10 shall be listed on the section 303 (d) list as impaired for phosphorus unless it exceeds 20 ug/L chlorophyll a for fewer than 30 percent of days during the summer sampling period of July 15 to September 15, as calculated following s. NR 102.56 (2) (c).

NR 102.60(4) (4) Stream phosphorus response indicators.

NR 102.60(4)(a) (a) General. A stream for which the total phosphorus concentration is within the combined approach range specified in Table 10 shall be listed on the section 303 (d) list as impaired for phosphorus unless it attains the phosphorus response indicators specified in this subsection. When applying the phosphorus response indicators for streams, the department may apply the benthic algal biomass indicator under par. (b) as a screening tool before determining whether the benthic diatom assessment under par. (c) is necessary for an attainment determination. If available, benthic diatom assessment results under par. (c) supersede results from the benthic algal biomass screening under par. (b).

NR 102.60(4)(b) (b) Benthic algal biomass screening. Benthic algal biomass is a measure of primary productivity in streams, and is quantified using a viewing bucket assessment method along stream transects. The benthic algal biomass phosphorus response indicator is applicable to both the aquatic life use and the recreational use, and may be used to make an initial use attainment determination as specified in Table 12. If results from the benthic algal biomass assessment conclusively demonstrate attainment or non-attainment of the benthic algal biomass indicator, no benthic diatom analysis under par. (c) is necessary for the attainment decision. If the benthic algal biomass assessment is inconclusive according to Table 12, or in cases where the assessment is inappropriate due to silted substrate, additional benthic diatom analysis under par. (c) is required to make the aquatic life use attainment determination. If a stream’s benthic algal biomass score is inconclusive and a benthic diatom sample is not available, the stream shall be proposed for inclusion on the section 303 (d) list.

Table 12

Stream benthic algal biomass phosphorus response
indicator

1 If the mean score is <1 but 20% or more of individual transect points score a 3, a benthic diatom assessment under par. (c) is required to make an attainment determination.

NR 102.60 Note Note: Wisconsin’s benthic algal viewing bucket methods are available on the department’s website in the Electronic Guidance and Documents (EGAD) system at https://apps.dnr.wi.gov/water/egadSearch.aspx by searching for Viewing Bucket Method for Estimating Algal Abundance in Wadeable Streams.

NR 102.60(4)(c) (c) Benthic diatoms. Benthic diatoms are an algal taxonomic group that represents primary producer community structure, and are used for assessment of the aquatic life use. This assessment is needed only if the benthic algal biomass assessment for aquatic life under par. (b) is inconclusive or inappropriate due to siltation. A stream’s diatom taxa are statistically analyzed using Wisconsin’s weighted average Diatom Phosphorus Index, or DPI. To determine use attainment, the DPI result shall be compared to the stream phosphorus criterion of 75 ug/L phosphorus. If only one diatom sample per site is available, the confidence interval approach described under s. NR 102.52 (2) (c) is applied. If the DPI is below 75 as specified under s. NR 102.52 (2) (c) 1., the phosphorus response indicator is attained. If more than one sample is available from the most recent 5 years, the mean score of the surveys is calculated and compared to the threshold of 75 ug/L without applying confidence intervals.

NR 102.60 Note Note: The statistical code to run the Wisconsin DPI calculation can be obtained through the department’s Water Evaluation Section by contacting the department’s call center at 1-888-WDNRINFo (1-888-936-7463) or using options provided on its website at https://dnr.wi.gov/contact/.

NR 102.60 History History: CR 19-094: cr. Register September 2022 No. 801, eff. 10-1-22.