More than 18,000 young fish have been released over the past two weeks to encourage angling.
The Environment Agency said releasing the fish would restore rivers and raise money through the sale of rod licences.
Breeds including barbel, bream and roach have been released across Teesside, County Durham and Northumberland.
The fish were reared at the agency’s national farm near Calverton, Nottinghamshire.
In Darlington, more than 1,600 barbel were released into the River Tees at Broken Scar and more than 2,300 roach into the River Skerne at South Park.
The agency also put almost 2,000 bream and 1,300 rudd into Lockwood Beck, near Guisborough.
A further 11,000 roach, bream, tench, crucian carp and rudd were released across Greencoft Pond near Annfield Plain, Wellfield Lake near Wingate, Hebron Lakes near Morpeth, Dissington Pond near Ponteland, Wydon Water at Hexham and Whittle Dene reservoir at Harlow Hill.
Fisheries officer Paul Frear said: “Restocking is one of many things we do together with our partners to develop fisheries, including reducing the impact of pollution, improving habitats and removing barriers to fish migration.
“We hope it will encourage more people to get out and enjoy fishing on the North East’s beautiful rivers.
“We target our work to rivers which may have suffered from previous pollution incidents or where there are barriers for fish passage.”