  We describe the statistical properties of two large river systems: the Danube
and the Mississippi. The properties of the two rivers are compared
qualitatively to the general properties of a critical steady state system.
Specifically, we test the recent suggestion by Bramwell, Fennell, Holdsworth
and Portelli [{\it Europhys. Lett.} {\bf 57}, 310 (2002)] that a universal
probability density function (PDF) exists for the fluctuations in river level,
namely the Bramwell-Holdsworth-Pinton (BHP) PDF. The statistical properties
investigated in this paper are: the PDF of the river flow and river level;
moment scaling with basin area; moment to moment scaling or relative scaling;
and power spectral properties of the data. We find that the moments of the flow
scale approximately with basin area and that the seasonally adjusted flows
exhibit relative moment scaling.
  Compared to the Mississippi, the Danube shows large deviations from spatial
scaling and the power spectra show considerable dependence on system size. This
might be due to water use and regulations as well as inhomogeneities in the
basin area.
  We also find that the PDF of level data in some, but not all, cases can be
qualitatively approximated by the BHP PDF. We discuss why this coincidence
appears to be accidental.
