The phosphorus (P) concentrations of suspended sediments determined by extraction with Cl resin (resin P), 0.1 N NaOH (NaOH P), and HClO4 (total sediment P), and from P desorption isotherms (intercept P) are presented and compared. The sediment concentrations representing 56 stormflows, sampled from two Pennsylvania agricultural watersheds over 4 years, were low and variable. Resin P and NaOH P constituted 9 and 38% of the total sediment P, respectively. Intercept P was highly correlated (r = 0.70) and closely estimated resin P, an index of readily desorbable labile and plant-available P. Both resin P (r = 0.75) and intercept P (r = 0.90) were highly correlated with the Equilibrium Phosphorus Concentration (EPC) but were consistently about 100 times more concentrated. NaOH P, an index of algal available P on sediment, was highly correlated with resin P (r = 0.73) and total sediment P (r = 0.87). Export of labile P (resin P plus total soluble P) in stormflow from both watersheds was mostly as soluble P (62–78%) and thus was controlled more by water than sediment export. Soluble P losses in total stream outflow (storm plus nonstorm) accounted for 50% of the algal-available P exported and about 30% of the total P exported from the 7.4 km2 watershed, suggesting that a P loss control strategy based only on erosion control would not be effective in these types of watersheds. About 42% of total sediment P and 57% of the total P exported from the 7.4 km2 watershed was estimated to be algal available.