Efforts are being made to maintain one of the last remaining strongholds for the freshwater pearl mussel.
Pearl mussels can live for more than 100 years
The number of pearl mussels in the north-east of England are dropping and breeding has also reduced.
The problem has become so severe that the Environment Agency has been forced to play matchmaker by relocating some of the mussels in the North Tyne.
The Agency hopes the new environment will encourage the pearl mussel to reproduce, ensuring its survival.
Pearl mussels are one of England's oldest river inhabitants and reproduce by the males releasing sperm into water which is then filtered by the females.
Fertilised eggs develop in the female's brood pouch for several weeks before the larvae are released into the water.
In healthy populations, many thousands of pearl mussels are found together in beds but fertilisation becomes near impossible when the dwindling shellfish populations are some distance apart.
Environment Agency conservation officer Anne Lewis said: "If the pearl mussels fail to revive their love life then the entire species will be extinct south of the Scottish border.
"We have relocated 40 pearl mussels to Kielder Hatchery and so far they are thriving, which is good news for the future."
The pearl mussel, which can live for more than 100 years, is extremely sensitive to water quality and habitat conditions. Illegal dredging and increased sedimentation have all taken their toll on the species.