The construction of the Gezhouba dam in 1981 on the Yangtze river also created a barrier to the migrating fish which further affected fish stocks.

BBC: Earth News - Giant fish 'verges on extinction'

In 1972, on the basis of data on toxicity to fish and migrating birds (but not to humans), the U.S. Environmental Protection Agency banned virtually all uses of DDT.

FORBES: Beyond Copenhagen

The agency says the area, near the Slimbridge Wetland Centre, is of "international importance" for migrating wildfowl, breeding waders, migratory fish and Atlantic eels.

BBC: Work carried out to protect Severn Estuary salt marshes