Lake Miami IA 04-LDM-1016

For the 2016 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Lake Miami are assessed (monitored) as "not supported" due to poor water transparency based on information from the ISU lake survey. Using the median values from these surveys from 2010-2014 (approximately 13 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 57, and 71 respectively for Lake Miami. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Miami in between the Eutrophic and the Hypereutrophic categories. These values suggest relatively low levels of chlorophyll a and suspended algae in the water, very 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 13 samples.

Note:  A TMDL for siltation and nutrients at Lake Miami was prepared by IDNR and approved by EPA in 2001; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle.   Because the Section 303(d) impairment for mercury in fish tissue was not addressed by the TMDL, this waterbody will be moved to IR Category 5a (impaired; TMDL needed) for the 2016 assessment/listing cycle.  

The level of inorganic suspended solids was very high at Lake Miami, and does suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in Lake Miami (16 mg/L) was ranked 128th among the 138 lakes by the ISU lake survey.

Data from the 2010-2014 ISU lake survey suggest a moderate population of cyanobacteria exists at Lake Miami. These data show that cyanobacteria comprised 84% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (11.9 mg/L) was ranked 36th of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to reduced water transparency related to the presence of common carp populations and sedimentation problems in the lake.   Information from the IDNR Fisheries Bureau suggests that turbidity remains an issue at this lake. Results of the ISU lake survey from 2010-2014 show there were no violations of the criterion for ammonia in 13 samples(0%), one violation of the criterion for dissolved oxygen in 13 samples(8%), and no violations of the criterion for pH in 13 samples(0%). 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 Lake Miami.

Fish consumption uses are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Miami in 2009 and 2010.   The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes.   The fish contaminant data generated from the 2009 RAFT sampling conducted at Lake Miami showed that levels of mercury were sufficiently high for concern and thus justified follow-up monitoring.   Results from the 2009 sampling show that the level of mercury in the sample of largemouth bass fillets (0.353 ppm) exceeded the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s revised (2007) fish consumption advisory protocol.   According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory.    Follow-up sampling conducted in 2010 showed that levels of mercury in largemouth bass (0.394 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm).    Thus a one meal per week fish consumption advisory was issued for Lake Miami and the fish consumption uses are assessed as “partially supported.”  Levels of primary contaminants in channel catfish were all below the advisory trigger levels: mercury: 0.109 ppm; total PCBs: 0.09 ppm; technical chlordane: <0.03 ppm.