Pickerel Lake IA 04-RAC-1180
Buena Vista County S1T93NR35W 4 mi NE of Marathon.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 6/13/2019 2:28:47 PM
- Updated
- 6/13/2019 2:40:40 PM
The Class A1 (primary contact recreation) uses are assessed (evaluated) as "not supported" due to high levels of algae that cause aesthetically objectionable conditions. The Class B(LW) aquatic life uses are assessed (evaluated) as "not supported" due to high levels of total suspended solids that leads to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life. High levels of algae at this wetland also suggest impairment. The fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. Sources of data for this assessment include results of water quality, aquatic vegetation, and fish monitoring conducted by the IDNR shallow lakes and wetlands monitoring program from 2014through 2016.
The Class A1 (primary contact recreation) uses are assessed (monitored) as "Fully supported." The Carlson’s (1977) trophic state index value for chlorophyll a was 24. According to Carlson (1977), the index value for chlorophyll a places Pickerel Lake in the oligotrophic category and suggests low levels of chlorophyll a and suspended algae in the water. This value suggests relatively low levels of chlorophyll a and suspended algae in the water and (monitored) "full support" of the aquatic life uses. Based on DNR's methodology, the median TSI value for chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Pickerel Lake will remain listed as "partially supported" for the 2018 assessment/listing cycle.
Results of water quality monitoring conducted at Pickerel Lake indicate that the aquatic life uses should be assessed (monitored) as "Fully supported" due to high levels of total suspended solids and algae at this lake. Guidelines for wetland assessment from the Upper Mississippi River Conservation Committee’s Water Quality Technical Section (2003) state that an average total suspended solids concentration during the growing season of less than 30 mg/L is necessary to provide sufficient water clarity to support the growth of submersed aquatic vegetation in wetlands and shallow lakes. High levels of total suspended solids impede the growth of submersed aquatic vegetation (SAV). Submersed aquatic vegetation is critical to the health of wetland and shallow lake ecosystems. The elimination of SAV can degrade habitat quality such that undesirable aquatic species such as cyanobacteria, common carp and fathead minnows dominate. As such, the suppression of SAV constitutes a violation of Iowa’s narrative water quality criteria protecting against undesirable or nuisance aquatic life.
Using the overall median values from the DNR shallow lakes and wetlands monitoring program from 2015 through 2016 (approximately 9 samples), the median growing season total suspended solids concentration was 4.75 mg/L; this median value does not exceed the UMRCC guideline. Thus, based on (1) suppression of SAV growth, (2) the resultant production of undesirable aquatic life, and (3) DNR’s assessment and listing methodology, the aquatic life uses at Pickerel are assessed as "Fully supported." Pickerel Lake was listed as "not supporting" its Class B(LW) uses due to violations of the UMRCC guideline for Turbidity: Siltation/Turbidity in the 2016 assessment cycle. According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Pickerel Lake will remain listed for the 2018 cycle as "not supporting" its Class B(LW) uses due to Turbidity: Siltation/Turbidity.
None listed