The WWF point out that:

‘wetlands are economically valuable biomes that provide goods and services upon which many communities and economies depend. Recognizing the economic importance of wetlands in addition to their biodiversity, scientific value, climate regulation, potential tourism, socio-cultural and other important wetland values is yet another good reason to reverse global wetland loss…

Dams disconnect rivers from their floodplains and wetlands. The damage to freshwater ecosystems can be devastating. They impact on the migratory patterns of fish, and flood riparian habitats, such as waterfalls, rapids, riverbanks and wetlands.

By slowing the movement of water, dams prevent the natural downstream movement of sediment to deltas, estuaries, flooded forests, wetlands, and inland seas, affecting species composition and productivity.

Dam operations also influence water quality. Water and sediment retention affect water quality and the waste processing capacity of rivers (the ability to break down organic pollutants). This could lead to production of toxic hydrogen sulphide gas that further degrades water quality.’