The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10030001 on the Upper Iowa River near Dorchester were as follows: the 2014 geometric mean was 127 orgs/100 ml, the 2015 geometric mean was 64 orgs/100 ml, and the 2016 geometric mean was 125 orgs/100 ml. One of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Eight of the combined 24 samples (33 %) 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 Iowa 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 at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

Results of chemical/physical water quality monitoring at DNR station 10030001 on the Upper Iowa River near Dorchester suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 0.4 mg/L), 36 Dissolved Oxygen samples (minimum = 7.9 mg/L), 36 pH samples (range = 7.8 to 8.5), 36 Temperature samples (maximum = 23.6°C), 36 Chloride samples (maximum = 20 mg/L), or 36 Sulfate samples (maximum = 22 mg/L) occurred during monitoring from January 2014 to December 2016. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

Fish consumption uses remain assessed (monitored) as “partially supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring near Dorchester in 2004, 2006, and 2010. 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. The composite samples of fillets from the 2004 samples of common carp and smallmouth bass had generally low levels of contaminants. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.228 ppm; total PCBs: 0.13 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.486 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. The levels of mercury in 2004 samples of both common carp and smallmouth bass exceed the DNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory: the level of mercury in the sample of common carp fillets was 0.228 ppm and in the sample of smallmouth bass fillets was 0.486 ppm.

The composite samples of fillets from the 2006 RAFT samples of golden redhorse (Moxostoma erythrurum) and smallmouth bass had similarly high levels of mercury. The level of mercury in the composite sample of golden redhorse fillets was 0.362 ppm, and the level of mercury in the composite sample of smallmouth bass fillets was 0.37 ppm. According to the DNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above an advisory trigger level in fillet samples, a consumption advisory will be issued. Because levels of mercury in both the 2004 and 2006 samples of smallmouth bass exceed the DNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory, a consumption advisory was issued for this segment by DNR in March 2008. Because level of mercury in the sample of the bottom-feeding golden redhorse was also greater than the advisory level, all species were included in the one-meal/week advisory. The existence of a one-meal/week consumption advisory for this assessment segment suggests that the fish consumption uses are “partially supported.” This advisory extends from the Lower Dam in eastern Winneshiek County upriver to County Road W20 approximately 5.5 miles upriver from Decorah. Follow-up sampling was conducted at the Upper Iowa River near Dorchester in 2010. The level of mercury in samples of golden redhorse fillets (0.318 ppm) and smallmouth bass fillets (0.392 ppm) were both above the advisory trigger level therefore suggesting that the fish consumption advisory should remain at this river segment.