High numbers of salmon have started leaping up the River Tyne in Northumberland.
Environmental experts are building a special fish passage to help them make their journey up the river to breed.
The Tyne is now one of the best salmon rivers in England and Wales - it was once very polluted.
The salmon run is when salmon swim from the ocean where they've spent most of their adult lives, to the rivers to have babies.
They often return to the same stretch of river where they were born.
Most salmon species do this journey during September through to November.
Eggs are laid by female fish in holes in the gravel.
After spawning many salmon die. Some do survive and some may spawn twice or more.
Eggs usually hatch during early spring.