Water quality issues throughout the USA has become an important focus, especially with recent environmental litigation involving land application of animal manure in the Illinois River Basin of northwest Arkansas and northeast Oklahoma.  The Illinois River Basin is a transboundary catchment draining from northwest Arkansas into northeast Oklahoma and has several municipal effluent discharges in the headwaters.  Historically, the phosphorus load was approximately 210,000 kg P yr^-1 and could be partitioned into municipal effluent discharges (~45%) and diffuse sources (~55%) including agriculture, urban and background.  Elevated dissolved and total P concentrations at the Illinois River near the Arkansas-Oklahoma border could be traced over 47 river km upstream to one municipal effluent discharge.  Recently, municipal effluent discharges have started managing on a P basis and have subsequently reduced effluent and stream P concentrations; thus, water quality conditions are improving at the Illinois River.  However, a small impoundment also exists near the border which has accumulated P rich sediments, and bottom sediment P release rates were extremely high under aerobic and anaerobic conditions which could act as future source of P to water column of the Illinois River.