Carter Lake IA 06-WEM-1714

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Carter Lake are assessed (monitored) as "Not supported" based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 53, 60, and 61 respectively for Carter Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Carter Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, very good water transparency, and moderately high levels of phosphorus in the water column. The data show 2 violations of the Class A1 criterion for pH in 15 samples. Carter Lake was listed as "not supported" its ClassA1 uses due to high levels of algal and non-algal turbidity that reduce water transparency and create aesthetically objectionable conditions in the 2014 assessment cycle. Based on IDNR's assessment methodology, median-based TSI values for both chlorophyll-a and Secchi depth must be 63 or less for two consecutive summer seasons before a lake can be removed from the state’s Section 303(d) list (IR Category 5). 

While the TSI values for Carter Lake are below the impairment trigger of 65 for the 2016 reporting cycle, Carter Lake was listed as "Not Supported" the Class A1 uses for the 2014 reporting cycle due to poor water transparency and aesthetically objectionable conditions caused by algae blooms.   Based on IDNR's assessment methodology, median-based TSI values for both chlorophyll-a and Secchi depth must be 63 or less for two consecutive summer seasons before a lake can be removed from the state’s Section 303(d) list (IR Category 5).    Therefore, Carter Lake remains assessed as "Not Supported" due to poor water transparency and aesthetically objectionable conditions caused by algae blooms for the 2016 assessment cycle.      

Note: A TMDL for algae/algal toxins, chlorophyll a, total phosphorus, total nitrogen, and pH at Carter Lake was prepared by IDNR and the Nebraska Department of Environmental Management and approved by EPA in 2007.   Because the 2009 TMDL includes not all of the impairments identified for the current (2016) assessment/listing cycle, this waterbody is not moved from IR Category 5a (impaired; TMDL approved) for the 2016 cycle.

The level of inorganic suspended solids was relatively low at Carter Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Carter Lake (2.5 mg/L) was ranked 39th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderately large population of cyanobacteria exists at Carter Lake. These data show that cyanobacteria comprised 86% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (26.8 mg/L) was ranked 84th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau, results from the ISU lake surveys, and results of a fish kill investigation in 2004.   Information from the IDNR Fisheries Bureau indicates that a fish fish renovation occurred on September 26, 2001.  2665 gallons of rotenone was applied and 89.6 tons of fish (Approximately 600 lbs./ac) were removed. Results from the ISU lake surveys show good water quality at Carter Lake.   Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 15 samples(0%), one violation of the criterion for dissolved oxygen in 15 samples(7%), and 2 violations of the criterion for pH in 15 samples(13%). Based on IDNR'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 Carter Lake. 

Carter Lake was assessed as "partially supporting" its Class B (LW) use in the 2008 reporting cycles due to significant violations to the dissolved oxygen criteria (5 violations in 22 samples).  Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on dissolved oxygen violations.   Because there have been two consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criteria, the Class B(LW) uses will be listed as "fully supported" for dissolved oxygen based on results of the ISU and UHL lake monitoring programs.  

Although attributed to "natural causes", the occurrence of fish kills in this lake in April 2004  and March 2010 is consistent with the assessment of aquatic life uses as “not supported.”  The first of the kills occurred on April 22, 2004.   The cause of the kill was identified as disease (virus).   An estimated 5,000 fish were killed; the kill affected only yellow bass.   No estimate of the value of the fish killed was provided.   The second of the kills occurred on March 5, 2010 and was attributed to natural causes (winterkill).   Approximately 100 fish were killed from what was suspected to be low dissolved oxygen due to thick ice and snow cover over the winter.   No estimate of the value of the fish was made. According to IDNR’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 IDNR 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.   Thus, this assessment segment will be placed in Category 2b of Iowa’s 2012 Integrated Report. 

Fish consumption uses remained assessed (monitored) as "partially supported" due to the continuation of a fish consumption advisory for this lake issued by the state of Nebraska due to high levels of PCBs (for more information, see the following web site:  http://www.deq.state.ne.us/SurfaceW.nsf/Pages/FCA.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   According to IDNR’s assessment methodology, the existence of a restricted consumption advisory indicates that fish consumption uses should be assessed as “partially supported.”

Note: According to Iowa DNR fisheries biologists, Carter Lake continue to see drastically improved water clarity as a result of the 2010 fishery renovation, alum treatment, dredging, wetland construction and 100 acre no wake zone. Toxic algae blooms have declined, phosphorous and nitrogen concentrations are lower, and water clarity has increased. Aquatic vegetation growth has been extreme and difficult to control particularly in the no-wake boating zone. The City of Carter Lake and Omaha have two mechanical weed harvesters.  Eurasian Water Milfoil (EWM) was discovered in the lake in 2015 and a whole lake treatment with sonar a.s. was done in the spring of 2016 in an attempt to eradicate EWM. Common carp are back in the system and eventually will have an impact on aquatic plants and water clarity.