Polychaeta is a class of macrobenthic fauna found in marine and estuarine environments. As part of a larger study of environment health impacts associated with the operation of a thermal power plant in the Na Thap River in Songkhla, Thailand, we examined bi-monthly organism densities of Polychaeta measured at each of five sites along the river downstream from the power plant for before and after its operation began. These densities, after log-transformation to reduce skewness with appropriate handling of zeroes, were found to be related to salinity measured at the same sites on the same occasions. There was also a statistically significant trend in the Polychaeta densities over the whole period.
