Beaver Lake IA 04-RAC-1182

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Beaver Lake are assessed (monitored) as "not supported" due to poor water transparency and 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 73, 73, and 79 respectively for Beaver Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Beaver Lake in the Hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column. The data show 3 violations of the Class A1 criterion for pH in 15 samples. While the pH values for Beaver Lake violations are not significantly greater than 10% of the samples for the 2016 reporting cycle, Viking Lake was listed as "partially supporting" the Class A1 uses for the 2014 reporting cycle due to pH.   Based on IDNR's assessment methodology, pH violations must be not significantly greater than 10% of the samples for two consecutive assessment cycles before a lake can be removed from the state’s Section 303(d) list (IR Category 4a).    Therefore, Beaver Lake remains assessed as "partially supported" due to violations of the criterion for pH for the 2016 assessment cycle.  

The level of inorganic suspended solids was moderately high at Beaver Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Beaver Lake (5.3 mg/L) was ranked 89th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a large population of cyanobacteria exists at Beaver Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (116.1 mg/L) was ranked 132nd of the 138 lakes sampled. This median is in the worst 25% of the 138 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 from 2010-2014. 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. 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 (monitored) as “partially supported” based on information from the IDNR Fisheries Bureau and results of the ISU lake surveys. Information from the IDNR Fisheries Bureau suggests that Beaver Lake has no vegetation due to a large grass carp population and excessive algae  and nutrients. Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and 3 violations of the criterion for pH in 15 samples(20%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples. While the pH values for Beaver Lake violations are not significantly greater than 10% of the samples for the 2016 reporting cycle, Viking Lake was listed as "partially supporting" the Class B(LW) uses for the 2014 reporting cycle due to pH.   Based on IDNR's assessment methodology, pH violations must be not significantly greater than 10% of the samples for two consecutive assessment cycles before a lake can be removed from the state’s Section 303(d) list (IR Category 4a).    Therefore, Beaver Lake remains assessed as "partially supported" due to violations of the criterion for pH for the 2016 assessment cycle.       

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.   EPA/IDNR fish contaminant (RAFT) monitoring at Beaver Lake in 2011 and 2012.    The composite samples of fillets from Largemouth Bass and channel catfish had low levels of contaminants.    Levels of primary contaminants in the 2011 composite sample of largemouth bass fillets were as follows: mercury: 0.257 ppm.  in 2012, the composite samples of fillets from largemouth bass contained 0.220 ppm mercury.    Levels of primary contaminants in the 2011 composite sample of channel catfish fillets were as follows: mercury: RESULT 0.0564; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.    The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.     The fish contaminant data generated from the 2011 and 2012 RAFT sampling conducted at this Beaver Lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.

Note:  A TMDL for algae and pH in this lake was prepared and approved by EPA in October 2014.   The approval of this TMDL moves the impairments due to algae and pH from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).