Abstract: A suspended sediment sensor system for determining concentrations of particles and their size distribution in a submitted fluid sample. The particles being measured range from 50-1000 microns in dimensions and the concentrations range from <50 to 50,000 parts per million (ppm) of fluid. Equipment used includes a fall tube, laser light source, light scattering detector system, optical equipment, and a system to control the movement of the sample and other fluid past the laser and detector system. The detector system measures background scatter from particles impinged upon by the laser source at an angle of about 165.degree.. Contemplated to be used with the foregoing is a computer and associated controls to allow an unattended in situ system for a river, lake, etc.