The acoustic attenuation coefficient in shallow coastal waters is of interest to designers and operators of devices such as naval mine-hunting sonars, sidescan surveying sonars, and acoustic Doppler current profilers, typically employing frequencies ranging from tens of kHz to several hundred kHz, possibly up to 1 MHz. At these frequencies attenuation due to suspended particulate matter which characterizes turbid coastal waters is an important contribution to the total attenuation coefficient. In this paper the effect of temperature, pressure, and salinity on the total attenuation coefficient for seawater containing a suspension of solid particles is investigated by employing suitable expressions for the sound speed, density, and viscosity of seawater as functions of temperature, salinity, and pressure. Results presented demonstrate that while there is little variation in the attenuation with pressure in up to a few hundred meters of water, there is significant variation with temperature and salinity over the ranges found globally in the sea.