Stress tolerance is the organism’s ability to withstand a certain amount of anthropogenic influences. The index range for each category is based upon a (0-10) scale, which is based mostly on the ability to withstand varying levels of dissolved oxygen and other chemical and physical disturbances. In some cases tolerance values are undetermined (U).
In the organisms describtion the scale will be depicted as follows:
Size range, Tolerance and Habitat - Example: S-M (L)(F), which shows an organism ranging in size from small (S) to medium (M), has a low tolerance (L) and lives is fast (F) aqautic environments.