Аннотация:The article presents the results of the test operation of a calculation–simulation complex (CSC)for level forecasting in a navigable branch in Don R. mouth area with daily lead-time (CSC Don-model). The main component of the CSC is a hydrodynamic model of the Don mouth area, combined with a model ofSea of Azov circulation. The quality of level forecasts is evaluated, and the main sources of forecast errors are identified.