The results of our investigation on the physicochemical forms of alpha-emitting radionuclides in bottom sediments sampled from the reservoir V-17 (Old Swamp, FSUE Mayak PA) are reported here. Alpha-Track radiography of the samples reveals the two types of the local alpha-emitting nuclide distribution among the bottom sands: a homogeneous distribution (less than 30 % of the total sum of alpha-activity) and an inhomogeneous one, concentrated in the single particles (at least 70 %). The size of the studied uranium particles varies from a couple of microns to tens of microns, with some of them reaching 100 pm in size, according to SEM analysis. Based on the results of EDX analysis, the composition of the U-containing particles represents mainly various uranium oxides/hydroxides without any significant contribution of other elements. X-Ray adsorption spectroscopy shows that the detected U particles are composed of UO 2; U 3O 8; (UO 2) 8O(OH) 1212(H 2O) or UO 3nH 2O (schoepite).