Lake Pahoja IA 06-BSR-1532

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "partially supported." Levels of indicator bacteria at Lake Pahoja Recreation Area Beach were monitored once per week during the primary contact recreation seasons (May through September) of 2014 (11 samples), 2015 (11 samples) and 2016 (14 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 Pahoja Recreation Area Beach, the geometric means from 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean from 2014, however, was greater than the Iowa water quality standard of 126 E. coli orgs/100ml and therefore suggests impairment of the Class A1 uses. The geometric mean was 186 E. coli orgs/100 ml in 2014, 48 E. coli orgs/100 ml in 2015 and 36 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 45% in 2014, 27% in 2015 and 14% in 2016. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2014 and 2015. 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 Pajoha are assessed (monitored) as "not supported" due to poor water transparency, aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 61, and 84 respectively for Lake Pajoha. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Pajoha in between the Eutrophic and the Hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and extremely high levels of phosphorus in the water column. The data show 2 violations of the Class A1 criterion for pH in 15 samples (13%).Additionally, according to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Lake Pahoja will remain listed for the 2018 cycle as "not supported" its Class A1 uses due to Chlorophyll a and pH.

The level of inorganic suspended solids was extremely low at Lake Pajoha, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Lake Pajoha (1.05 mg/L) was ranked 2nd among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at Lake Pajoha. These data show that cyanobacteria comprised 95% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.6 mg/L) was ranked 58th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on results of a fish kill investigation in September of 2012. The fish kill occurred on or before September 14, 2012. An unknown number of fish were killed on June 7, 2011, and the kill was attributed to natural causes (low DO and elevated levels of ammonia), thus placing Lake Pahoja in category 3b: waters in need of further investigation. According to the DNR assessment/listing 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 (2012-2014) 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.”Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills 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 "not supported" due to violations of the Class A1, B(LW) criterion for pH.Results of the ISU lake survey from 2012-2016 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 2 violations of the criterion for pH in 15 samples(13%). 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 Pajoha.According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Lake Pahoja will remain listed for the 2018 cycle as "not supported" its Class A1 uses due to pH.

Note: A Fisheries renovation in 2013 was performed to remove common carp. Water quality has improved significantly since the renovation. Aquatic plants have returned. Nuisance cyanobacteria blooms still present but less frequent. Water quality improvement is expected in the coming years.

NOTE: A TMDL for impairments at Lake Pahoja due to algae and pH was prepared by Iowa DNR and approved by the U.S. EPA in 2018. Thus, the impairments of Class A1 uses due to algae and pH, and the impairment of the Class B(LW) uses due to pH, are moved from IR Category 5a (impaired and TMDL required) to IR Category 4a (impaired; TMDL not required).