Lake Keomah IA 03-SSK-930

Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Lake Keomah Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (16 samples), 2013 (17 samples) and 2014 (17 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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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).

At Lake Keomah Beach, the geometric means from 2012, 2013 and 2014 were all below the Iowa water quality standard of 126 E.  coli orgs/100 ml.   The geometric mean was 122 E.  coli orgs/100 ml in 2012, 58 E.  coli orgs/100 ml in 2013 and 77 E.  coli orgs/100 ml in 2014.   The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E.  coli orgs/100 ml) was 31% in 2012, 18% in 2013 and 29% in 2014.   The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2012 and 2014.   According to IDNR's assessment methodology and U.S.  EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Keomah are assessed (monitored) as "partially supported" due to aesthetically objectionable conditions caused by algae blooms based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 65, and 70 respectively for Lake Keomah. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Keomah in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and very high levels of phosphorus in the water column. The data show 2 violations of the Class A1 criterion for pH in 15 samples. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on pH violations.  There were less than 10% of the samples exceeding the single-sample maximum criterion.   Therefore, the impairment (4a) for pH is suggested for delisting for the 2016 assessment/listing cycle.

Note: A TMDL for siltation at Lake Keomah was prepared by IDNR and approved by EPA in 2002; thus, this lake was placed into IR Category 4a for the 2004 assessment/listing cycle.   In September 2012, IDNR received EPA approval of a TMDL for the impariments of the Class A1 and Class B(LW) uses caused by algae and pH.   Thus, these impairments were moved to IR Category 4a for the current (2016) IR cycle.   Not all of the section 303(d) impairments identified for the current (2016) assessment/listing cycle (indicator bacteria, mercury, and dissolved oxygen), however, are addressed in the TMDL.   Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the 2016 assessment/listing cycle.  

The level of inorganic suspended solids was low at Lake Keomah, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Lake Keomah (2 mg/L) was ranked 10th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderately large population of cyanobacteria exists at Lake Keomah. These data show that cyanobacteria comprised 92% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (29.1 mg/L) was ranked 92nd of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "not supported" due to violations of the Class B(LW) criterion for DO. Results of the ISU lake survey from 2010-2014 show there were 2 violations of the criterion for ammonia in 15 samples(13%), 4 violations of the criterion for dissolved oxygen in 15 samples(27%), and 2 violations of the criterion for pH in 15 samples(13%). Based on IDNR's assessment methodology these violations are significantly greater than 10% of the samples and therefore suggest impairment (not supported/monitored) of the Class B(LW) uses of Lake Keomah. Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the single-sample maximum criterion are necessary to propose delisting based on pH violations.  There were less than 10% of the samples exceeding the single-sample maximum criterion.   Therefore, the impairment (4a) for pH is suggested for delisting for the 2016 assessment/listing cycle.

The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU surveys from 2010-2014 show that nitrate levels are low at this lake (maximum value = 2.5 mg/l; median = 0.2 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses. 

Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Keomah in 2009 and 2010.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   The fish contaminant data generated from the 2009 RAFT sampling conducted at Lake Keomah showed that levels of mercury were sufficiently high for concern and thus justified follow-up monitoring.   While levels of mercury, total PCBs, and technical chlordane in the 2009 composite samples of channel catfish fillets were all below the advisory trigger level, results from this sampling showed that the level of mercury in the sample of largemouth bass fillets (0.464 ppm) exceeded the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol.   According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory.    Follow-up sampling conducted in 2010 showed that levels of mercury in largemouth bass (0.432 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm).    Thus a one meal per week fish consumption advisory was issued for Lake Keomah, and the fish consumption uses were assessed as “partially supported.”  This assessment remains for the 2014 IR cycle.