The National Rivers Water Quality Network (NRWQN) includes routine measurement of three optical variables: visual clarity, turbidity, and coloured dissolved organic matter (CDOM; indexed by the filtrate absorption coefficients at 440 and 340 nm). The purpose of this add-on to the NRWQN was to see if it was possible to develop a simple Multiple linear regression (MLR) model of light penetration into river waters as a function of the routine optical measures so as to predict lighting at the river bottom. The dataset was further extended by measurements on five rivers on the west coast South Island , three large glacial-flour laden alpine rivers, and two small wetland-fed lowland rivers with very high CDOM. The dataset was published as Davies-Colley & Nagels (2008). [Davies-Colley, R.J.; Nagels, J.W.(2008). Predicting light penetration into river waters. Journal of Geophysical Research Vol. 113, G03028, doi:10.1029/2008JG000722.]