English: Schematic showing the construction of streams (tributaries) on a fish ladder, so as to provide a diverse range of environments for a variety of (predatory) insects. The idea is similar to making insect hotels but then for aquatic insects.

The main reasons why pond networks can provide much environmental benefit and restore some of the aquatic biodiversity are:

• streams get straightened more and more in developing countries, and have been straightened allready in many developed countries. This means that there are few bends where fish can rest, deposit eggs, provide housing for aquatic insects, ...
• at the main streams, there can be a lot of ship traffic. The movement of the ships, aswell as the continued removal of detritus and aquatic plants (oxygen plants, free-floating plants, submerged plants, ...) by the government means that there is little life anymore within the main streams. The pond networks hence provide the required safe refuges for the fauna. In addition, PN 2 absorbs some of the detritus in it's stream. This means there will be less clean-up work to maintain the transport function of the main river, and also wastes less biomass (biomass is efficiently used by the fauna)
• at some points in the country, the ecosystem allready no longer works optimally (due to the missing of those aquatic organisms the pond networks would support). Thic could create problems over time if the issue is not adressed (all organisms rely on each other in a food chain and are all essential). Besides the falling apart of the ecosystem, it also allows gives the space to exotic species to thrive. Some of these (e.g. Anopheles mosquitoes rather than say Chironomidae, Culicidae and Simulidae mosquitoes) can be very annoying to the human population (carrier of diseases as malaria, ...).
• the pond networks can be easily closed off in the event of an accident (e.g. chemical spill, ...). This makes sure not all fauna/flora gets impacted by the spill, and hence allows the river to recover much faster.

Some examples of what organisms would live in which pond network (example for Europe):

• Mayflies (Ephemeroptera): PN2
• Stoneflies (Plecoptera): PN1
• Dragonflies and damselflies (Odonata): PN1
• Water bugs (Heteroptera): PN2
• Alderflies, Fishflies, Dobsonflies (Megaloptera): PN2
• Beetles (Coleoptera): PN1 and PN2 (depends on type of insect in family)
• Caddisflies (Trichoptera): PN1 and PN2
• Flies, Mosquitoes (Diptera): PN2

Note: in the event the (freshwater) river connects to the sea, the mouth can be disconnected from the sea; see this image