Blue Lake IA 06-WEM-1728

Assessment Comments

Assessment is based on results of (1) IDNR beach monitoring program from 2002-04, (2) ISU lake survey from 2000-04, (3) ISU reports on lake plankton communities, 2000-05, and (4) information from IDNR Fisheries Bureau and Wildlife Bureau.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting" due to aesthetically objectionable conditions related primarily to high levels of inorganic turbidity and secondarily to blooms of suspended algae.   Results of IDNR beach monitoring during the 2002-04 period do not suggest impairment of the Class A uses at this lake.   The Class B(LW) aquatic life uses remain assessed (evaluated) as "fully supporting".   Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring.   The sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2002, 2003, and 2004, (2) results from ISU lake surveys from 2000 through 2004, (3) ISU reports on plankton communities at Iowa lakes from 2000 through 2004, and (4) information from the IDNR Fisheries Bureau.  

EXPLANATION:  Results of IDNR beach monitoring at Blue Lake from 2002 through 2004 suggest that the Class A uses should be assessed (evaluated) as “partially supported."  Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2002 (30 samples), 2003 (29 samples), and 2004 (16 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 A (primary contact recreation) uses:  (1) all thirty-day geometric means for 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 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A uses should be assessed as “not supported”.   Also, if 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 A uses should be assessed as “partially supported”.   This assessment approach is based on U.S.  EPA guidelines (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

At Blue Lake beach, the geometric means of all 63 thirty-day periods during the summer recreation seasons of 2002, 2003 and 2004 were below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   These results suggest generally very low levels of indicator bacteria at this lake.   None of the 59 samples collected during recreational seasons of 2002 and 2003 exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   During the 2004 recreational season, 2 of 16 samples exceeded this criterion.   Based on IDNR’s assessment methodology, however, the results for the 2004 recreational season do not suggest that significantly more than 10 percent of the samples exceed Iowa’s single-sample maximum criteria,  Thus, these results do not suggest an impairment of the Class A uses of Blue Lake.  

Results from the ISU statewide survey of Iowa lakes suggest that high levels of turbidity related primarily to and inorganic suspended solids impair the Class A uses of Blue Lake.   Using the overall median values from this survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 68, 65, and 73, respectively.   According to Carlson (1977), the index values for total phosphorus and chlorophyll-a place this lake in the range between eutrophic and hyper-eutrophic lakes; the index value for Secchi depth places this lake in the lower range of hyper-eutrophic lakes.   These index values suggests moderately high levels of phosphorus in the water column, moderately high levels chlorophyll-a, and very poor water transparency.  

According to Carlson (1991), the occurrence of a low chlorophyll-a TSI value relative to those for total phosphorus and secchi depth indicate non-algal particles or color dominate light attenuation.   The ISU lake data suggest that non-algal particles do likely limit algal production at Blue Lake.   The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2004 was 5.2 mg/l.   Of 131 lakes sampled, Blue Lake had the ninth highest median level of inorganic suspended solids (21.0 mg/l), thus suggesting that non-algal turbidity limits the production of algae.   These conditions suggest an ongoing impairment to the Class A (primary contact) uses primarily due to presence of high levels of inorganic turbidity that violate Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.   The TSI value for chlorophyll-a (65) is on the border of impairment; the lake also had the 22nd highest TSI value for chlorophyll-a.   These results suggest that suspended algae also contributes to aesthetically objectionable conditions at Blue Lake.   The IDNR Fisheries Bureau concurs that turbidity-related impairments exist at this lake.   Other factors may limit algal production at Blue lake.   Based on median values from ISU sampling from 2000-04, the ratio of total nitrogen to total phosphorus for this lake is 12; this ratio suggests the possibility that algal production at this lake may be limited by nitrogen availability.  

Nuisance aquatic (algal) species (i.e., bluegreen algae) do not appear to be a problem at Blue Lake.   Data from the ISU survey from 2000-04 suggest that bluegreen algae (Cyanophyta) comprise a relatively small portion (approximately 10%) of the summertime phytoplankton community of this lake.   The average per sample mass (biovolume) of bluegreen algae in summers of 2000 through 2004 at this lake (3.6 mg/l) was the 17th lowest of the 131 lakes sampled.   These conditions do not suggest any impairments due to presence of nuisance aquatic (e.g., algal) species.  

The Class B(LW) aquatic life uses of this lake are assessed (evaluated) as "fully supported " based on information from the DNR Fisheries Bureau and DNR Wildlife Bureau.   Also, the ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected, or for pH in the 15 samples collected, during summers of 2000 through 2004.   These results suggest good chemical/physical water quality at Blue Lake.  

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