Rathbun Reservoir - South Fork Arm IA 05-CHA-2027

Sources of Data:

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Class A1 - Lake TSI's

Class BWW1 - Conventional Parameters:

Class BWW1 - Toxic Parameters:

Class BLW - Additional Information:

The Class B(WW-1) aquatic life uses of this arm of Rathbun Reservoir are assessed (monitored) as “partially supported” due to the impact or poor water quality (water transparency) on the lake’s fish populations. A comparison of water quality data to production of the primary sport fish at Rathbun Reservoir (crappie) suggests only “partial support” of the aquatic life uses of the South Fork Arm. In 2006, the DNR Fisheries Bureau summarized approximately 35 years of data on abundance of crappies at Rathbun Reservoir. These data were combined with the available water quality data (707 Secchi depth readings) from that 35-year period to determine the spatial and temporal differences in crappie abundance and water quality conditions within Rathbun Reservoir.

Based on the Secchi depth readings and the analysis of crappie production for the period 1970-2006, the best water clarity and crappie production occurs near the dam and in central portion of the main lake basin where Secchi depths average approximately one meter. Of the main arms of the reservoir, the Honey Creek Arm typically has the best crappie production and best water transparency (average Secchi depth of 0.66 m), followed by the Buck Creek and Chariton arms (average of 0.5 m), and South Fork Chariton arm (average of 0.3 m). The poorest crappie production occurs in the Chariton and South Fork arms. The reduced water transparencies and relatively poor crappie production in the arms of the reservoir is attributed primarily to greater influence of nonpoint source runoff from the reservoir’s watershed on the water quality in the reservoir’s arms. Additional sources of turbidity in the reservoir’s arms include re-suspension of bottom sediments and wave action. In summary, results of the analysis of fisheries and water quality data at Rathbun Reservoir suggest that (1) poor water quality (transparency) in adversely affects the reservoir’s sport fish populations, (2) the aquatic life uses of the Chariton and South Fork arms are impaired due to high levels of turbidity, and (3) improving water transparency through control of nonpoint source runoff (i.e., through implementation of best management practices (BMPs)) could provide significant benefits to the sport fishery of this reservoir. Based on this information, the Class B(WW-1) aquatic life uses of the South Fork Arm are assessed (monitored) as “partially supported.”

Class HH-F - Toxic Parameters: