Lake Macbride IA 02-IOW-629

Results of IDNR beach monitoring from 2012 through 2014 suggest that the Class A1 uses are "Fully Supported." Levels of indicator bacteria at Lake Macbride Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2012 (20 samples), 2013 (15 samples) and 2014 (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 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 Macbride 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 11 E.  coli orgs/100 ml in 2012, 27 E.  coli orgs/100 ml in 2013 and 55 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 5% in 2012, 20% in 2013 and 20% in 2014.   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 "Fully Supported" of the Class A1 uses. While the levels of indicator bacteria for Lake Macbride Beach are not significantly greater than 10% of the samples and do not exceed the state's single season geometric mean criterion of 126 E.  coli orgs/100 ml for the 2016 reporting cycle, Lake Macbride Beach was listed as "partially supporting" the Class A1 uses for the 2014 reporting cycle due to indicator bacteria.   Based on IDNR's assessment methodology, indicator bacteria violations must be not violation for two consecutive assessment cycles before a lake can be removed from the state’s Section 303(d) list (IR Category 5a).    Therefore, Lake Macbride Beach remains assessed as "partially supported" due to violations of the criterion for indicator bacteria for the 2016 assessment cycle.

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Macbride are assessed (monitored) as "partially supported" due to poor water transparency 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 65, 64, and 61 respectively for Lake Macbride. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Macbride in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and moderately high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was low at Lake Macbride, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Lake Macbride (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 Macbride. These data show that cyanobacteria comprised 95% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (31.7 mg/L) was ranked 97th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported”  due to a fish kill that on June 7, 2011.  Chemical water quality at Lake MacBride, however, appears to be improving as the pH impairment is suggested for de-listing.  An unknown number of fish were killed on June 7, 2011, and the kill was attributed to natural causes (high water temperatures and the presence of a blue-green algae bloom, thus placing Lake MacBride in category 3b: waters in need of further investigation.  According to IDNR's assessment methodology, 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 (2010-2012) 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.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2010-2014 show there were one violation of the criterion for ammonia in 15 samples(7%), 3 violations of the criterion for dissolved oxygen in 15 samples(20%), and one violation of the criterion for pH in 15 samples(7%). Based on IDNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Lake Macbride.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring at Lake MacBride in 2007 and turtle tissue monitoring in 2009.   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: mercury: 0.179 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.   Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.0627 ppm.   Levels of primary contaminants in the samples of shoulder tissue from snapping turtle were as follows: mercury: 0.113 ppm; 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 and turtle contaminant data generated from the 2007 and 2009 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.

Note:  A TMDL for nutrients and siltation at Lake MacBride was prepared by IDNR and approved by EPA in 2005.    Because, however, the Section 303(d) impairment due to indicator bacteria  and  Do violations at this lake were not addressed in the TMDL, this lake is placed in IR Category 5a (impaired; TMDL required).