Arrowhead Pond IA 06-WED-1702

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Arrowhead Pond 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 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 69, and 71 respectively for Arrowhead Pond. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Arrowhead Pond in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and very high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 14 samples.

The level of inorganic suspended solids was moderately high at Arrowhead Pond, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Arrowhead Pond (3.5 mg/L) was ranked 78th 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 Arrowhead Pond. These data show that cyanobacteria comprised 45% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.4 mg/L) was ranked 57th of the 138 lakes sampled.

A fish kill that occurred in this lake on July 26, 2005, however suggests "impairment" of the Class B(LW) uses. The kill was identified as a summer kill due to low levels of dissolved oxygen related to an algal die-off. According to the DNR investigation, approximately 500 bluegill, 1,500 yellow bass, and 600 channel catfish (including all cage catfish at this lake) were killed. The estimated value of the fish killed was $39,000. This is the same assessment as that developed for the 2010, 2012, 2014, and 2016 assessment/listing cycles. The continuance of the IR Category 3b listing is based on DNR's 2012 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 (2014-2016) 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 3b and will be added to the state list of waters in need of further investigation. Thus, this assessment segment will remain in Category 3b of Iowa’s 2018 Integrated Report.

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.

Note:A TMDL for siltation at Arrowhead Pond was prepared by DNR and approved by EPA in 2001. Not all Section 303(d) impairments identified for the 2018 assessment/listing cycle (algae), however, are addressed in the TMDL. Thus, this waterbody remains in IR Category 5a (impaired; TMDL required) for the 2018 assessment/listing cycle.