Submerged orifices are an important feature of state-of-the art fingerling protection facilities being installed at certain low-head dams on the Columbia and Snake Rivers. Some systems require up to 60 orifices. One problem with the orifices is the tendency for debris to accumulate across their entrances. This debris can cause damage to fish that must pass through the orifice to reach the safety of a bypass channel. Because the orifices are submerged, they cannot be easily inspected. Timely elimination of debris requires constant surveillance at great expense. This research and development program was initiated to develop a method of automatically detecting debris when it begins to accumulate at the entrance to any orifice. Earlier studies demonstrated that electronic load cells (strain gauges) would detect debris (Jensen and Long 1983). The objective of the studies under the current contract is to verify that the Orifice Debris Sensor (ODS) can reliably detect small quantities of debris over the broad range of hydraulic conditions likely to be encountered at dams.