Due to their physical properties, illite clays can sorb cesium-137 almost irreversibly and, therefore, sequester contamination from the environment. However, applying large amounts of clay to natural aquatic habitats for in situ remediation purposes may create problematic conditions due to high turbidity and sedimentation. To evaluate potential effects of turbidity from illite application on survivorship of stream fish, yellowfin shiners (Notropis lutipinnis) and tessellated darters (Etheostoma olmstedi) were subjected to treatment with two different types of clay in flow-through simulated stream raceways.  Turbidity and fish mortality was subsequently monitored for seven days. At 2-m downstream from the application point, mean turbidity peaked during clay application at 525 and 72 nephelometric turbidity units (NTU) in the air-floated illite and semi-dry illite treatments, respectively. Turbidity returned to levels similar to that of the controls (4-6 NTU) after four hours in the air-floated illite raceways and one hour in the semi-dry illite raceways. Although the majority of the suspended clay was quickly flushed from the system and the remaining settled to the bottom, turbidity did continue to fluctuate because of fish movements and sediment resuspension. Fish mortality did not significantly differ among control and illite treated raceways.