<p>The potential for sediments in the Lake Urmia basin to sorb and retain dissolved inorganic phosphorus (P) is unknown. Land use has impacted Sediment P sorption capacity along several tributaries to Lake Urmia and its wetlands. The following hypotheses were tested: (1) upstream agricultural P sources are more significant than downstream locations, (2) the storage of P and its subsequent release is controlled by potential differences in physicochemical properties of upstream versus downstream sediments, and (3) the differences in algae growth will correlate with its native adsorbed P (NAP) and equilibrium values (EPC₀). We employed several strategies to link sediment physicochemical properties, sediment P adsorption characteristics, and potential algal response to understand upstream and downstream P cycling characteristics better. The results suggest that P sorption capacity was generally higher in the downstream sediments than in upstream locations. There was a significant correlation between sediment properties, mainly clay and organic matter, and sorption parameters. The equilibrium phosphorus concentration (EPC₀) values were higher than the soluble reactive phosphorus (SRP) concentration in the water column, suggesting that sediment is a source of P in the water column. River sediments have a high potential for P sorption and, depending on the landscape and biogeochemical processes can be considered an internal source of pollution in the river system.</p>