In order to assess over time the conditions of the spawning gravels, we collect sediment samples. First, an area stream is carefully dug out, and then all of the collected rocks are taken back to the laboratory. These samples are then separated by the size of the components present. The results tell the scientists whether there are cobbles of appropriate size for spawning and if the fine sediment levels are appropriate for the survival of young fish emerging from the eggs.

Sediment data also includes what is called "pebble counts." This is where 100 randomly selected stream rocks are measured to determine the mean size of the substrate. This tells the scientists if the gravel size is appropriate for spawning and helps track whether the sediments of a watercourse are becoming finer or courser.