Native, acid and alkali pretreated dried Potamogeton crispus (P. crispus) was used for adsorption of Reactive Red 198 from aqueous solution. Effects of physicochemical environment on adsorption were investigated. The surface charge of the native, acid and alkali treated biomass were determined to be zero at pH 4.6, 3.8 and 4.1 +/- 0.1, respectively. Adsorption capacity of native biomass was increased with alkali treatment against native and acid pretreated biomass. The maximum adsorption capacities (q(max)) at 20 degrees C of native. acid and alkali pretreated biomass were determined as 14.3, 26.8 and 44.2 mg g(-1), respectively. FT-IR analysis shows that P. crispus has many functional groups such as COO, S=O, C-N, N-H. These functional groups can react with dye molecule in solution. Pseudo-second-order and intraparticle diffusion kinetic models are applicable adsorption of RR198 by P. crispus since adsorption of RR198 is complex and involves more than one mechanism. (C) 2011 Elsevier B.V. All rights reserved.