Lake Macbride IA 02-IOW-629

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Lake Macbride Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (15 samples), 2015 (18 samples) and 2016 (15 samples), as part of the DNR beach monitoring program. According to DNR’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 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 55 E. coli orgs/100 ml in 2014, 122 E. coli orgs/100 ml in 2015 and 44 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 20% in 2014, 44% in 2015 and 27% in 2016. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2015 and 2016. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Macbride are assessed (monitored) as "partially 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 2012-2016 (approximately 21 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 66, and 63 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 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 2 violations of the Class A1 criterion for pH in 21 samples (10%).

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 (1.6 mg/L) was ranked 9th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Lake Macbride. These data show that cyanobacteria comprised 89% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (30.9 mg/L) was ranked 100th 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 DNR'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 DNR 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 2012-2016 show there were no violations of the criterion for ammonia in 21 samples(0%), 2 violations of the criterion for dissolved oxygen in 21 samples(10%), and 2 violations of the criterion for pH in 21 samples(10%). Based on DNR'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.

Note: A TMDL for nutrients and siltation at Lake MacBride was prepared by DNR 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).