  We investigate flow dynamics in rivers characterized by basin areas and daily
mean discharge spanning different orders of magnitude. We show that the delayed
increments evaluated at time scales ranging from days to months can be
opportunely rescaled to the same non-Gaussian probability density function.
Such a scaling breaks up above a certain critical horizon, where a behavior
typical of thermodynamic systems at the critical point emerges. We finally show
that both the scaling behavior and the break up of the scaling are universal
features of river flow dynamics.
