Blue Lake IA 06-WEM-1728

Assessment Comments

Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010 (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.

Basis for Assessment

SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to poor water clarity mainly caused by large amounts of suspended solids, but secondarily caused by the presence of aesthetically objectionable blooms of algae.   The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the DNR Fisheries Bureau.   Fish consumption uses remain “not assessed.”  Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2008, 2009, and 2010 (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), and (4) information from the IDNR Fisheries Bureau.

Note:  A TMDL for the algae and turbidity impairments at Blue Lake was prepared by IDNR and approved by EPA in January 2009.   Because the 2009 TMDL includes all of the impairments identified for the current (2012) assessment/listing cycle, this lake will remain in IR Category 4a (impaired; TMDL approved) for the 2012 cycle.  

EXPLANATION: Results of IDNR beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “fully supported."  Levels of indicator bacteria at Blue Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (13 samples), 2009 (16 samples), and 2010 (15 samples) as part of the IDNR beach monitoring program.   According to IDNR’s assessment methodology two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) the geometric mean of the samples from each recreation season of the three-year assessment period are less than the state’s geometric mean criterion of 126 E.  coli orgs/100 ml and (2) not more than 10% of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E.  coli orgs/100 ml.   If a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.”  Also, if significantly more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E.  coli orgs/100 ml, the Class A1 uses should be assessed as “partially supported.”  This assessment approach is based on U.S.   EPA guidelines (see pgs 3-33 to 3-35 of U.S.   EPA 1997b).    

NOTE:  Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed.   Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season.   Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake.   Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches.   Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion.  This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.  

At Blue Lake beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 63 E.  coli orgs/100 ml in 2008, 58 E.  coli orgs/100 ml in 2009, and 53 E.  coli orgs/100 ml in 2010.   The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E.  coli orgs/100 ml) was 23% in 2008, 13% in 2009 and 7% in 2010.   None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses.   According to IDNR’s assessment methodology and U.S.  EPA guidelines, these results suggest “full support” of the Class A1 uses.  

Results of the ISU lake survey and UHL ambient lake monitoring program however suggest that the Class A1 uses are “not supported” at Blue Lake due to poor water transparency mainly due to high levels of suspended sediment and secondarily aesthetically objectionable algae blooms.  Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 64, and 68 respectively for Blue Lake.   According to Carlson (1977) the index value for Secchi depth places Blue Lake in the hypereutrophic category, while the values for chlorophyll a and total phosphorus place Blue Lake in between the eutrophic and hypereutrophic categories.   These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column.  

The median concentration of inorganic suspended solids is very high and contributes to the impairment at Blue Lake.   Results from the ISU and UHL lake surveys show that the median level of inorganic suspended solids in Blue Lake from 2006-2010 was 11.7 mg/L, which was the 14th highest concentration of the 134 lakes monitored by these programs.

Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Blue Lake, which contributes to an impairment at this lake for nuisance aquatic life.   These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (45.6 mg/L) was also the 29th highest of the 134 lakes sampled.   This median is in the worst 25% of the 134 lakes sampled.    The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life.    This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2006-2010 period.    Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment.    No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria.    The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.    

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau.   Information from the IDNR Fisheries Bureau suggests that Blue Lake has a poor recreational fishery and a large carp population.   Results from the ISU and UHL lake surveys suggest "full support" of the Class B(LW) (aquatic life) uses.  The ISU and UHL lake survey results show good chemical water quality at Blue Lake.   During 2006-2010 there were no violations of the Class B(LW) criterion for dissolved oxygen (22 samples).   There was one violation of the Class B(LW) criterion for ammonia (22 samples) and one violation of the Class A1,B(LW) criterion for pH (22 samples).   Based on IDNR’s assessment methodology, these violations are not greater than 10% of the samples and therefore do not suggest an impairment of water quality at Blue Lake.  

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.