The paper presents a method of recommended waterway parameters determination, based on modified relationships derived from actual empirical research - the authors’ combination of PIANC and Canadian deterministic methods and stochastic relationships). These relationships are mostly discontinuous functions (e.g. of ship type variable, speed, method of determining the position, etc.), which can be approximated by continuous spline functions. Application built in C# allows determining the recommended minimum width of the waterway, the width increase due to the accuracy of the vessel positioning method, and the minimum radius of waterway bends. The results can be further utilized in the Decision Support System for Water Transport Safety.