It is debatable which reflects long term pollution trends better - fish or insects. A combination of both surveys can be very valuable and enlightening.
Fish shocking is used to gather a fair representation of the diversity of the fish population. In this method, electrical current is run through the water, momentarily stunning the fish which are then swept up in nets. the photograph on the overview page illustrates a group employing fish shocking.
The electrodes are attached to a large backpack which holds an electrical generator. The current follows through the water between the two hand-held electrodes. The number of people required to conduct a successful fish-shocking is determined by the size of the waterway. The must be enough people to follow along behind the electrodes to capture the shocked fish in nets as well as people carrying water-filled buckets. The buckets are used to deposit fish into while the fish shocking takes place. Most fish recover quickly from the shock and can be returned to the stream after counting with no ill effects.
The distance covered as well as the length of time should be recorded during a fish shocking. It is important to have trained professionals conduct or assist in this type of assessment to make sure that the equipment is operated safely and correctly with no harm coming to either fish or humans.