The high moisture content of an aquatic biomass was used advantageously in a hydrothermal process. Reducing sugars, amino acids, proteins, and crude oil were extracted from water lettuce (Pistia stratiotes L.) using subcritically heated water. The highest yields of reducing sugars and amino acids were obtained after treatment at 473 K for 30 min (23.70 +/- 0.52 g kg(-1) and 4.35 +/- 0.09 g kg(-1) dry mass respectively), while protein was obtained at 3.60 +/- 0.04 g kg(-1) feedstock after treatment at 523 K for 60 min. The greatest solubilization occurred at 523 K after 60 min. The solid residues could be applied as fertilizers as hemicellulose and cellulose were hydrothermally converted to humus. The crude oil components that were extracted from the liquid residues differed markedly between the two treatment temperatures. The conversion of furan compounds to cyclopentenone and its derivatives only occurred at the higher reaction temperature and was increased by a longer reaction time. (C) 2011 Elsevier Ltd. All rights reserved.