South Fork Iowa River IA 02-IOW-748
from confluence with unnamed tributary in SE 1/4 NE 1/4 S2 T87N R21W (SE of Logsdon Park) Hardin Co. confluence with unnamed tributary in W 1/2 S19 T88N R21W Hardin Co.
- Cycle
- 2020
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 6/4/2020 9:05:57 AM
- Updated
- 10/12/2020 12:58:11 PM
The Class BWW1 aquatic life use was assessed as “partially supported” based on biological sampling data. All other designated uses were "not assessed".
Sources of
Data: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 BIO See Below 21 South Fork Iowa River Iowa Falls – Logsdon Co Park Iowa DNR 6 BIO See Below 380 South Fork Iowa River Buckeye – REMAP #79 Class A1 - No Data Class
BWW1 - Biological Sampling: Benthic
Macroinvertebrates: BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal BM Sample Gear BMIBI score BMIBI Class 47b BMIBI BIT BMIBI Pass/ Fail 21 8/9/16 121 47b MS/WW Hess 41 Fair 62 Fail 380 9/18/14 113 47b MS/WW Hess 45 Fair 62 Fail 380 8/21/14 113 47b MS/WW Hess 51 Fair 62 Fail 380 8/21/14 113 47b MS/WW ArtSub 33 Fair 62 Fail Fish: BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal Riffle Stream? FIBI score FIBI Class 47b FIBI BIT FIBI Pass/ Fail 21 8/9/16 121 47b MS/WW Yes 59 Good 53 Pass 380 9/18/14 113 47b MS/WW No 78 Excellent 32 Pass Overall: Community Assessment Type Assessment Result Support Level Earned IR Category Actual IR Category Reason Benthic
Macroinvertebrates Monitored Fail (0/4) Partial Fish Monitored Pass (2/2) Full Overall Monitored Fail Partial 5bv 5bv Assessment
is monitored because all samples were collected in the last five years. Class BWW1 – Continuous Monitoring: The results of continuous dissolved oxygen (DO) and temperature monitoring in 2013 and 2014 for the DNR/SHL stream biological sampling projects were marginally acceptable for fully supporting the Class BWW1 aquatic life use. The lowest DO concentration recorded in 109 days of continuous monitoring was 2.3 mg/L. The daily DO minimum concentration failed to meet the 24-hour DO criterion (5 mg/L) in 11 of 109 days and the 16-hour DO criterion (5 mg/L) in 3 of 109 days. The 2013 and 2014 combined percentage exceeding the 24-hour DO criterion (10.1%) was slightly greater than (failing) the 10% impairment threshold used to assess conventional water quality parameters; however, the associated statistical analysis confidence level was not high (<90%). The 2013 and 2014 combined percentage exceeding the 16-hour DO criterion (0%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). The maximum stream temperature recorded during the sensor deployment period was 33.2 degrees (C). The temperature criterion for warmwater interior streams (32 C) was exceeded in 3 of 109 days. The percentage exceeding (2.8%) was less than (passing) the 10% impairment threshold with high statistical confidence (>90%). Based on these data, the BWW1 aquatic life use is assessed as not impaired by DO and temperature. The DNR’s continuous monitoring assessment methodology specifies that the frequency of violations must exceed the 10% threshold with greater than 90% statistical confidence in order to assess the aquatic life use as impaired. The assessment type is considered as “monitored” because the data meet the minimum requirements of the DNR’s continuous monitoring assessment methodology. Because of the contradictory results showing DO violations in the first year (2013) and not the second year of monitoring (2014), additional continuous monitoring of DO and temperature is strongly recommended. Class BWW1 – Fishkill Assessment: The Class BWW1 use previously resided in IR Category 3b based on the assessment developed for the 2009 fish kill. Because no additional fish kills were reported in this segment for at least 10 years post fish kill (2019), the IR Category for the fish kill assessment was changed from 3b to 3a (water not assessed). DNR believes that any impact from the fish kill from which the impairment was based has likely dissipated. Class HH - No data