Thousands of fish have been relocated into parts of the River Trent affected by a pollution incident 14 months ago.
About 18,000 roach, barbel and dace have been released into two sites on the Trent, at Stone and Rugeley.
In October 2009, thousands of fish died in a 30-mile (48 km) stretch of water between Stoke-on-Trent and Yoxall after a leak of cyanide and raw sewage.
The Environment Agency (EA) said more fish re-stocking would take place next year.
All of the new fish were about 18 months old and came from the Environment Agency's fish farm in Calverton, Nottingham.
EA officers said the fish would not suffer any shock by being placed in the cold waters, although the temperature in the river was only just above 4C (39F).
The fish will start spawning in 12 months' time.
Cyanide entered the Strongford Sewage Treatment Works in Stoke-on-Trent in October 2009.
An investigation has been launched into the cause of the pollution incident.
The EA said it would still be seeking prosecutions and the investigation was continuing.
Red Industries Ltd, a waste company based in Burslem, Stoke-on-Trent, was banned from discharging industrial effluent into sewers immediately after the leak.
The firm said at the time that it voluntarily stopped before the suspension notice was served.