Better understanding of the origin, transport and fate of nitrogen and phosphorus in Midwestern watersheds within the Great Lakes basin is critical for improved management of aquatic ecosystems.  While much research has been conducted on reach-scale processing and transport of N and P in streams, relatively little research has been directed toward understanding the impact of dams and their associated impoundments on nutrient dynamics in the affected river systems.  Even less research has focused on the interactions between stream reaches and impoundments.  To better understand these nutrient dynamics, we investigated two predominately agricultural watersheds in southeastern Michigan, the Huron (2,330 km²) and Raisin (2,780 km²), both draining into the western end of Lake Erie.  Nutrient budgets of the two watersheds show more nutrient retention in the more heavily impounded catchment.  Paired sampling sites above and below impoundments as well as above and below selected stream reaches demonstrate most nutrient retention is occurring in impoundments.  Simulation modeling using SWAT indicates that altering the occurrence and position of these impoundments can play an important role on their nutrient retention effectiveness.