The paper describes a relatively easy to use computer program for the analysis of steady state surface and energy profiles in networks of open channels. RIVER4 is intended primarily for use in a time-sharing environment to facilitate the trial and error setup and calibration and modification of networks of arbitrary geometry and connectivity. The networks may consist of natural and man-made open channels or sewer systems or both, in configurations of single reach, multiple tributaries, and bifurcated branches with resultant "island" flow. As well as regular reaches, the system description may include transition devices such as bridges, weirs, culverts, manholes, and diversion structures. The flow resistance equation is selected at run time, from six commonly used laws. System geometry is stored on secondary devices such as tapes or discs so that relatively large systems may be analysed in machines of modest size. Key words: backwater, channel, computer, design, flood, islands, networks, profiles, sewers.