To appear in Control Engineering Practice, 2007 Anti-windup for marginally stable plants and its application to open water channel control systems L. Zaccarian, Y. Li, E. Weyer, M. Cantoni and A. Teel Abstract Actuator saturation can have a significant impact on control system performance. In particular, when actuators saturate because of large initial condition mismatch at startup, or because of large disturbances, the controller can suffer from so-called integrator windup. This paper describes the application of recent anti-windup and bumpless transfer (AWBT) compensation techniques to the problem of open-water channel control. This is non-trivial in light of the (marginally) unstable nature of uncontrolled open water channels, which for the purposes of controller design, can modelled as a concatenation of integrators, linked by saturation-prone gates used to regulate the flow of water. AWBT compensator design is considered within the context of both continuous- and discrete-time controllers and models. All simulation studies are carried out using an experimentally validated, high-fidelity model of the Haughton Main Channel in Queensland, Australia. The AWBT compensation schemes considered achieve excellent performance. Key words: Anti-windup, bumpless transfer, multi-variable control, marginally stable system, open water channels, LQ control, H-infinity loop-shaping.