Lost Island Lake IA 06-LSR-1632

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lost Island Lake are assessed (monitored) as "fully supported" 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 62, 61, and 66 respectively for Lost Island Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lost Island Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

DNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest de-listing of an impairment. The Secchi depth TSI value for the 2002 assessment listing cycle was 70, which based on DNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions. Because the TSI value for the 2016 assessment/listing cycle was less than the trigger of 65 (2016 listing for Secchi depth a was 63), and because the TSI value for the current listing cycle is also 62, based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (4a) for Secchi depth is suggested for delisting for the 2018 assessment/listing cycle.

The level of inorganic suspended solids was moderately high at Lost Island Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Lost Island Lake (5.19 mg/L) was ranked 96th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a large population of cyanobacteria exists at Lost Island Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (76.2 mg/L) was ranked 127th of the 138 lakes sampled. This median is in the worst 25% of the 138 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa's narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values from 2012-2016. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. Assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to a fish killd on June 9, 2007 and September 29, 21013. The kill in June of 2017 was identified as a natural fish kill of crappies due to post-spawning stress.The fish kill occurred on or before September 29, 21013.Investigators counted 74 walleyes, mostly very large fish with some approaching 10 pounds dead along the shoreline. The majority of the walleyes, especially the largest females, had extensive amounts of fungus present on their bodies and in and around their mouths. Lost Island Lake, like many lakes in the area, experienced very warm water temperatures in late summer and early fall. Walleyes become stressed in warm water with the largest fish most likely experiencing the greatest impact. The onset of a bacterial/fungal infection probably occurred around this time and culminated late last week with rapidly changing weather conditions.According to DNR’s 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 (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.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to supportadditionto the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 3b and will be added to the state list of waters in need of further investigation.

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 no violations of the criterion for pH in 15 samples(0%). 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 Lost Island Lake.

Note: Alake restoration project beginning in 2008 and isstill ongoing.