More than 5,000 fish are to be released into a County Durham lake and the River Tyne in Northumberland in an effort to encourage breeding.
Environment Agency staff will release 4,200 fish into Strawberry Fields Fishery, near Seaham, in County Durham, and 3,000 into the Tyne at Hexham.
The move follows studies which showed there might be too few fish to survive another bad winter.
The fish come from the agency's farm at Calverton, in Nottinghamshire.
Teams will release 3,000 roach into the Tyne at Hexham and 2,000 roach, 2,000 crucian carp, and 200 tench into Strawberry Fields Fishery.
The agency has used information from angling competitions to see how fish populations are performing in various locations.
An agency spokesman said: "Breeding and survival can sometimes be a problem for fish over the winter, and occasionally we need to add more fish into local still-waters and rivers.
"But it's good news for local anglers as it means that there should be a wider variety of healthy adult fish to catch next season.
"Hopefully in the long term it helps to establish a stronger natural population of fish across the region."