Snyder Bend Lake IA 06-WEM-1734

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Snyder Bend Lake are assessed (monitored) as "not 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 83, 67, and 75 respectively for Snyder Bend Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Snyder Bend Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, extremely poor water transparency, and extremely high levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

The level of inorganic suspended solids was extremely high at Snyder Bend Lake, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Snyder Bend Lake (30 mg/L) was ranked 137th 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 Snyder Bend Lake. These data show that cyanobacteria comprised 78% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (18.8 mg/L) was ranked 76th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to two fish kills in 2004 and 2005.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 Snyder Bend Lake.

The second of these kills occurred on or before July 18, 2005. The kill was attributed to natural causes (high water temperature). An estimated 65 fish were killed; all the fish were northern pike of from 3 to 15 pounds. No estimate of the value of the fish killed was provided. Because northern pike are susceptible to high water temperatures, and because other species were not affected, the kill was attributed to high water temperature (85F). Although unrelated to the kill, the lake area received 0.7-inch of rainfall the evening prior to the kill.

This is the same assessment as that developed for the 2008, 2010, 2012, 2014, and 2016 assessment/listing cycles. The continuance of the IR Category 3b listing is based on DNR's assessment methodology that states the followingthe 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 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. Thus, this assessment segment will remain in Category 3b of Iowa’s Integrated Report.

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

Note:Lake bathymetry was changed in 2011 when the lake was inundated by flood waters. The lake was additionallybecame infested with Asian carp during this event.