This was answered in two steps. Step 1 modeled the effectiveness of grassed waterways in the Clear Creek watershed. Step 2 examined the degree to which water quality is related to grassed buffers in typical Iowa watersheds. Results from Clear Creek show properly designed and constructed grassed waterways are highly effective in maintaining water quality in runoff regardless of cropping systems. Results from typical streams show only a weak relationship exists between water quality and buffer strips. It is unclear why th two results are inconsistent with one another. Explanations range from possible experimental flaws--e.g., grassed waterways in step 1 verses buffer strips in step 2--to geological-induced differences from one location to the next to the possibility of there being a lag time between when runoff quality improves to when stream quality improves.