A 3D non-isotropic algebraic stress/flux turbulence model is employed to simulate turbulent buoyant helicoidal flow and heat transfer in a rectangular curved open channel. The prediction shows that, unlike the isothermal flow, there are two major and one minor secondary flow eddies in a cross section of thermally stratified turbulent buoyant helicoidal flow in a curved open channel. The results compare favorably with available experimental data. The thermocline in a curved channel is thicker than that in a straight channel. All of these is the result of complex interaction between the buoyant force, the centrifugal force and the Reynolds stresses. The turbulent flow in a curved channel is obviously nonisotropic: the turbulence fluctuations in vertical and radial directions are lower in magnitude than that in the axial direction, which illustrates the suppression of turbulence due to buoyant and centrifugal forces. The results are of significant practical value to engineering works such as the choice of sites for intake and pollutant-discharge structures in a curved river. (C) 2003 Elsevier Science Ltd. All rights reserved.