Assessment Comments
Assessment is based on results of (1) the IDNR-county beach monitoring program from 2006, 2007, and 2008, (2) fish kill investigations in April 2005 and August 2006, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2008.
Basis for Assessment
SUMMARY: The Class A1 primary contact recreation uses are assessed (monitored) as "fully supported" based on indicator bacteria data from the IDNR county beach monitoring program. The Class B(LW) aquatic life uses of this waterbody are assessed (evaluated) as “partially supported” due to a fish kill in April 2005 and a fish kill in August 2006. Both kills were attributed to natural causes. This impairment is appropriate for Class 2b of the integrated report. The fish consumption uses are assessed (monitored) as "fully supported." Sources of data for this assessment include: (1) the IDNR-county beach monitoring program from 2006, 2007, and 2008, (2) fish kill investigations in April 2005 and August 2006, and (3) results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2008.
EXPLANATION: Results of IDNR county beach monitoring from 2006 through 2008 suggest that the Class A1 uses are assessed (monitored) as "fully supported." Levels of indicator bacteria at Grays Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2006 (18 samples), 2007 (14 samples), and 2008 (10 samples) as part of the IDNR-county beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. 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 A1 uses should be assessed as “not supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Grays Lake beach, the geometric means of all thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 6% in 2006, 0% in 2007 and 20% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
The Class B(LW) aquatic life uses, however, are assessed (evaluated) as "partially supported" due to fish kills at Grays Lake. The first kill occurred on or before April 14, 2005. The kill was attributed to “unknown/natural” causes. IDNR field staff investigated this kill. An estimated 30 fish were killed (all largemouth bass); no estimate of the value of the fish killed was provided. The dead largemouth bass were found from west of the beach to the northwest boat launch. Most of the bass were about 6 inches long; a few were up to 9 inches, and a couple were about 2 inches in length. A light wind was blowing from the southeast and likely concentrated the dead fish at this end of the lake. Water quality testing did not identify any obvious causes of the kill. The IDNR Fisheries Bureau suggested that the kill could have been caused by a virus or may have even resulted from winterkill.
The second fish kill occurred on or before August 16, 2006. The kill was attributed to "unknown/natural" causes. The total number of fish killed was 89. The estimated value of these fish was $589.94. No evidence was found to indicate the cause of this fish kill.
The fish kill portion of this assessment is the same as that developed for the 2008 assessment/listing cycle. The continuance of the IR Category 2b listing is based on IDNR's 2010 assessment methodology that states the following: the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2006-2009) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated” and will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Thus, this assessment segment will remain in Category 2b of Iowa’s 2010 Integrated Report.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Grays Lake in 2008. The composite samples of fillets from channel catfish and largemouth bass had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: 0.094 ppm; and technical chlordane: 0.055 ppm. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.089 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 2008 RAFT sampling conducted at this 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.
