Des Moines River IA 04-LDM-1012

The Class A1 (primary contact recreation) uses are assessed (monitored) as "fully supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 51 samples collected during the recreational seasons of 2014 through 2016 at ISU/ACOE station 0.7 mi downstream from Red Rock Dam were as follows: the 2014 geometric mean was 9 orgs/100 ml, the 2015 geometric mean was 6 orgs/100 ml, and the 2016 geometric mean was 7 orgs/100 ml. None of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. None of the combined 51 samples (0%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because none of the recreation seasons geometric means exceeded criteria for Class A1 uses, these uses are assessed as "fully supported."

Results from this ISU/ACOE monitoring station also suggest that the Class B(WW1) aquatic life uses are "fully supported"; however, the Class B(WW1) aquatic life uses remained assessed as "not supported" due to reoccurring fish kills in this river segment. No violations of Class B(WW1) water quality criteria for conventional parameters (dissolved oxygen, pH, ammonia-nitrogen) occurred in the 66 samples collected at this station during the 2014-2016 monitoring period. In addition, analysis of four samples for metals showed no violations of the respective Class B(WW1) criteria for copper. These results suggest “full support” of the Class B(WW1) aquatic life uses.

The Des Moines River immediately downriver from Red Rock Dam has a history of fish kills caused by gas bubble trauma. For the period 1983 though 2013, 33 kills in the Red Rock Dam tailwater area have been attributed to gas bubble trauma (Lutz 2014). Fish kills caused by gas bubble trauma occur due to a large imbalance between the concentrations of atmospheric gasses in the water and the levels of these gasses dissolved in the blood of the fish. The concentrations of dissolved gasses such as oxygen and nitrogen in river water tend to equal the concentrations in the blood of a fish. When the levels of atmospheric gasses dissolved in river water become very high (i.e., super-saturated)—such as can happen when water moves through or over a large dam—the levels of these gasses will also rise in the blood of fish. As long as fish can stay in deeper water, the hydrostatic (water) pressure will keep these gasses fully dissolved in the fish’s blood. If, however, the flow of water downstream from the dam is decreased suddenly, the depth of the water will also decrease. With shallower water, fish are not able to move to deeper areas to keep the hydrostatic pressure sufficiently high to keep the gasses fully dissolved in their blood. During these conditions, the gasses dissolved in the fish’s blood will gradually come out of solution as bubbles, and these bubbles will interfere with blood circulation. Symptoms of gas bubble trauma in fish include gas blisters on the skin at the margins of the scales and as pop-eye (exophthalmia) where the eyes of the fish distend from the eye sockets. In the extreme case, blood circulation is disrupted to the point that fish kills occur.

One fish kill due to gas bubble trauma was reported during the 2012-14 assessment period; the most recent kill occurred on August 8, 2013. According to the DNR assessment/listing methodology, two consecutive IR cycles (five years) showing full support are needed before an existing impairment can be proposed for de-listing. Thus, due to reoccurring fish kills caused by gas bubble trauma, and due to the history of this type of fish kill in this river reach, the Class B(WW1) aquatic life uses remain assessed as "not supported” and will remain in IR Category 4c (i.e., impairment due to a non-pollutant stressor; TMDL not required).

Fish contaminant monitoring conducted downstream from Red Rock Reservoir by ISU/ACOE in 2012, 2013, and 2014 showed low levels of contaminants (dieldrin, heptachlor epoxide, chlordane, alachlor, and trifuluralin) in composite samples of whole fish common carp. Levels of PCBs in composite whole-fish carp samples for all Aroclors analyzed in from 2012 to 2014 (1016, 1221, 1232, 1242, 1248, 1254, and 1260) were all below levels of detection. Detection levels for PCB were high in all three years; thus, data for PCBs are inconclusive. The history of low levels of PCBs in fish from this river segment, however, suggest that PCB levels are below the one meal per week advisory trigger of 0.20 ppm for total PCBs (sum of Aroclors 1248, 1254, and 1260).

Composite samples of fillets from a predator species were analyzed for mercury in all three years. In 2012, the composite sample of largemouth bass fillets had low levels of mercury (0.14 mg/kg). The average levels of mercury in the composite sample of smallmouth bass fillets in 2013 was 0.10 ppm. Results were not reported for levels of mercury in the 2014 composite sample of predator fish. Levels of mercury in the samples from this river segment from 2012 and 2013 were below the one meal per week advisory threshold for mercury (0.30 ppm). Based on this information, fish consumption uses are assessed (monitored) as "fully supported".

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 2014, 2015, and 2016 ISU/ACOE samplings (or from previous ISU/ACOE monitoring) conducted in the segment of the Des Moines River immediately downstream from Red Rock Reservoir show that levels of contaminants (PCBs, chlordane and mercury) do not exceed any of the IDPH/DNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.

In addition, analysis of nine samples for metals showed no violations of the respective Class HH (Human Health)criteria for copper. These results also suggest “full support” of the Class HH (Human Health)uses.