 The paper discusses the potential of data assimilation, DA, in improving hydrologic predictions, but notes that advances in research have not been adequately implemented in operational forecast systems. This is due to challenges such as quantifying uncertainty and efficiently merging data and models. A hydrologic DA workshop was held in Delft, the Netherlands, which led to a review of current status and potential hurdles in transitioning DA research into cost-effective operational tools. The paper discusses several related aspects, including theoretical aspects in DA algorithms, uncertainty estimation, new observations, real-time control of water resources systems, and community-based generic DA tools. It is recommended that cost-effective transition from research to operation should be facilitated by developing community-based modeling in DA tools and fostering collaborative efforts among hydrologic modelers, DA developers, and operational forecasters. This article was authored by YLU, A.H. Wirts, M. Clark, and others. We are article.tv, links in the description below.