Draft California 2026 Integrated Report (303(d) List/305(b) Report)

Supporting Information

Regional Board 1 - North Coast Region

Water Body Name:	Big River Beach at Mendocino Bay
Water Body ID:	CAC1133004520081013235216
Water Body Type:	Coastal & Bay Shoreline


DECISION ID	161306	Region 1
Big River Beach at Mendocino Bay

Pollutant:	Indicator Bacteria
Final Listing Decision:	Delist from 303(d) list (TMDL required list)
Last Listing Cycle's Final Listing Decision:	Do Not Delist from 303(d) list (TMDL required list)(2018)
Revision Status	Revised
Reason for Delisting:	Applicable WQS attained; according to new assessment method
Impairment from Pollutant or Pollution:	Pollutant

Regional Board Conclusion:	In accordance with section 6.1.5.3 of the Listing Policy, data should be representative of the critical timing that the pollutant is expected to impact the waterbody. Lacking constant inputs, indicator bacteria do not persist in the environment for a long period and effects are of relatively short duration. As a result, the historic levels of bacteria in the waterbody may be a poor indicator of current risks to human health, particularly when more recent data are available to sufficiently assess the water quality standard. Historic lines of evidence for data collected prior to October 21, 2012, were evaluated pursuant to these considerations and were not used to assess water quality standards attainment because they do not meet the temporal representation requirements of section 6.1.5.3 of the Listing Policy. This pollutant is being considered for removal from the CWA section 303(d) List under section 4.2 of the Listing Policy. Under this section a single line of evidence is necessary to assess listing status. Seventeen lines of evidence are available in the administrative record to assess this pollutant. Geometric means are used to assess the data for the REC-1 beneficial use. Where geometric means are not available, statistical threshold values are used. Geometric means are available for Big River Beach at Mendocino Bay and will be used for the assessment. *DO NOT LIST REC-1 BENEFICIAL USE* For Fecal Coliform, 0 of 1 single sample maximum exceeds the objective for the REC-1 beneficial use, and this is insufficient data to the allowable frequency for AB411 beaches in the Listing Policy. For Enterococcus, 0 of 65 geometric means exceed the objective for the REC-1 beneficial use, and this does not exceed the allowable frequency of AB411 beaches in the the Listing Policy. For Total Coliform, 3 of 7 monthly percents exceed the objective for the SHELL beneficial use, and this is insufficient information to apply Table 3.2 of the Listing Policy. DELIST SHELL BENEFICIAL USE* *For Total Coliform, 0 of 7 weekly medians exceed the objective for the SHELL beneficial use, and this is insufficient information to apply Table 3.2 of the Listing Policy and does not exceed the allowable frequency in Table 4.2 of the Listing Policy. Based on the readily available data and information, the weight of evidence indicates that there is sufficient justification for removing this water segment-pollutant combination from the CWA section 303(d) List. This conclusion is based on the staff findings that: 1. The data used satisfies the data quality requirements of section 6.1.4 of the Policy. 2. The data used satisfies the data quantity requirements of section 6.1.5 of the Policy. 3. For Fecal Coliform, 0 of 1 single sample maximum exceeds the objective for the REC-1 beneficial use, and this is insufficient data to the allowable frequency for AB411 beaches in the Listing Policy. For Enterococcus, 0 of 65 geometric means exceed the objective for the REC-1 beneficial use, and this does not exceed the allowable frequency of AB411 beaches in the the Listing Policy. For Total Coliform, 3 of 7 monthly percents exceed the objective for the SHELL beneficial use, and this is insufficient information to apply Table 3.2 of the Listing Policy. For Total Coliform, 0 of 7 weekly medians exceed the objective for the SHELL beneficial use, and this is insufficient information to apply Table 3.2 of the Listing Policy and does not exceed the allowable frequency in Table 4.2 of the Listing Policy. 4. Pursuant to section 4.11 of the Listing Policy, no additional data and information are available indicating that standards are not met.

Regional Board Decision Recommendation:	After review of the available data and information, RWQCB staff concludes that the water body-pollutant combination should be removed from the section 303(d) list because applicable water quality standards for the pollutant are not being exceeded.

State Board Review of Regional Board Conclusion and Recommendation:

State Board Decision Recommendation:

Line of Evidence (LOE) for Decision ID 161306, Indicator Bacteria	Region 1
Big River Beach at Mendocino Bay

LOE ID:

353518

Pollutant:

Enterococcus

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

GeoMean

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data to determine beneficial use support and the results are as follows: 0 of the 36 samples exceeded the geomean water quality standard for Enterococcus. This is a six week rolling geomean that is calculated weekly.

Data Reference:

WQ from the BeachWatch for the 2026 Integrated Report in Region 1

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial in ocean waters applies a six-week rolling geomean to enterococcus, not to exceed 30 cfu/100mL. (Ocean Plan 2019)

Objective/Criterion Reference:

SWRCB. 2005. Water Quality Control Plan, Ocean Waters of California (Ocean Plan). California Environmental Protection Agency, State Water Resources Control Board. February 2, 2019

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): Big River

Temporal Representation:

Data was assessed for samples collected within 10 years of the close of data solicitation for the 2026 Integrated Report (October 21, 2012 to October 21, 2022).

Environmental Conditions:

QAPP Information:

QAPP for BeachWatch

QAPP Information Reference(s):

QAPP Reference for Beach Watch Program

Line of Evidence (LOE) for Decision ID 161306, Indicator Bacteria	Region 1
Big River Beach at Mendocino Bay

LOE ID:

353464

Pollutant:

Total Coliform

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Percent

Beneficial Use:

Shellfish Harvesting

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data to determine beneficial use support and the results are as follows: 3 of the 7 samples exceeded the water quality standard for Total Coliform. The water quality standard for shellfish is based on the percent of Total Coliform at each station that exceed 230 per 100 mL, and is calculated on a monthly basis.

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

California Ocean Plan (SWRCB 2018) states that not more than 10 percent of the samples shall exceed 230 per 100 mL.

Objective/Criterion Reference:

California Ocean Plan Water Quality Control Plan Ocean Waters of California 2009

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): Big River

Temporal Representation:

The samples were assessed for the ten years before the close of data solicitation (2012-10-21 to 2022-10-21).

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.

Line of Evidence (LOE) for Decision ID 161306, Indicator Bacteria	Region 1
Big River Beach at Mendocino Bay

LOE ID:

353463

Pollutant:

Total Coliform

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

Median

Beneficial Use:

Shellfish Harvesting

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data to determine beneficial use support and the results are as follows: 0 of the 7 samples exceeded the water quality standard for Total Coliform. The water quality standard for shellfish is based on the median concentration of Total Coliform at each station, and is calculated on a monthly basis.

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

California Ocean Plan (SWRCB 2018) states that the median concentration of total coliform samples shall not exceed 70 per 100 ml.

Objective/Criterion Reference:

California Ocean Plan Water Quality Control Plan Ocean Waters of California 2009

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): Big River

Temporal Representation:

The samples were assessed for the ten years before the close of data solicitation (2012-10-21 to 2022-10-21).

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.

Line of Evidence (LOE) for Decision ID 161306, Indicator Bacteria	Region 1
Big River Beach at Mendocino Bay

LOE ID:

321970

Pollutant:

Fecal Coliform

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

SSM

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed BeachWatch_Mendocino County data for Big River Beach at Mendocino Bay to determine beneficial use support and the results are as follows: 0 of the 1 samples exceeded the water quality threshold for Coliform, Fecal. The water quality threshold is based on a Single Sample Maximum (SSM) value that is calculated daily. This data is for an AB411 beach. This LOE specifically corresponds with dry weather samples and only includes samples collected between April 1 and October 31 of each year.

Data Reference:

WQ from the BeachWatch for the 2026 Integrated Report in Region 1

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial use in ocean waters applies a single sample maximum of fecal coliform, not to exceed 400 per 100 mL. (Ocean Plan 2019)

Objective/Criterion Reference:

SWRCB. 2005. Water Quality Control Plan, Ocean Waters of California (Ocean Plan). California Environmental Protection Agency, State Water Resources Control Board. February 2, 2019

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): Big River (Big River-Big River-Mendocino Bay Headlands SP, Mendocino).

Temporal Representation:

The samples were collected between the days of 2022-07-26 and 2022-07-26 .

Environmental Conditions:

QAPP Information:

QAPP for BeachWatch

QAPP Information Reference(s):

QAPP Reference for Beach Watch Program

Line of Evidence (LOE) for Decision ID 161306, Indicator Bacteria	Region 1
Big River Beach at Mendocino Bay

LOE ID:

353517

Pollutant:

Enterococcus

LOE Subgroup:

Pollutant-Water

Matrix:

Water

Fraction:

GeoMean

Beneficial Use:

Water Contact Recreation

Number of Samples:

Number of Exceedances:

Data and Information Type:

PATHOGEN MONITORING

Data Used to Assess Water Quality:

Water Board staff assessed Beachwatch_Mendocino County data to determine beneficial use support and the results are as follows: 0 of the 29 samples exceeded the geomean water quality standard for Enterococcus. This is a six week rolling geomean that is calculated weekly.

Data Reference:

Mendocino County Beachwatch data reformatted and renamed to match CEDEN fields.

SWAMP Data:

Non-SWAMP

Water Quality Objective/Criterion:

The bacteria water quality objective to protect the REC-1 beneficial in ocean waters applies a six-week rolling geomean to enterococcus, not to exceed 30 cfu/100mL. (Ocean Plan 2019)

Objective/Criterion Reference:

SWRCB. 2005. Water Quality Control Plan, Ocean Waters of California (Ocean Plan). California Environmental Protection Agency, State Water Resources Control Board. February 2, 2019

Evaluation Guideline:

Guideline Reference:

Spatial Representation:

The samples were collected at 1 monitoring site(s), station(s): Big River

Temporal Representation:

Data was assessed for samples collected within 10 years of the close of data solicitation for the 2026 Integrated Report (October 21, 2012 to October 21, 2022).

Environmental Conditions:

QAPP Information:

Data exempt from QAPP requirement. Draft QAPP for Mendocino County Beachwatch data used instead. Represents data collection procedure prior to development of a formal QAPP.

QAPP Information Reference(s):

Draft QAPP for Mendocino County Beachwatch. Represents data collection procedure prior to development of a formal QAPP.