Current advances in many-core technologies demand simulation algorithms suited for the corresponding architectures while with regard to the respective increase of computational power, real-time and interactive simulations become possible and desirable. We present an OpenCL implementation of a Lattice-Boltzmann-based free-surface solver for GPU architectures. The massively parallel execution especially requires special techniques to keep the interface region consistent, which is here addressed by a novel multipass method. We further compare different memory layouts according to their performance for both a basic driven cavity implementation and the free-surface method, pointing out the capabilities of our implementation in real-time and interactive scenarios, and shortly present visualizations of the flow, obtained in real-time.