An EA officer spotted the fish during a routine patrol at Costa Beck, north of Malton in North Yorkshire.
The fish was dead, however, and was sent to EA scientists in York for examination. The fish weighed 8lb and was thought to have been dead for about three days following spawning.
Further investigations of the scales revealed that the fish had spent two years in freshwater before entering the sea for two years and finally returning to the river at the end of last summer.
Shaun McGinty, fisheries officer for the Derwent, said: “This is a fantastic find. We suspected that there were one or two salmon in the Derwent and after last summer’s surveys we knew that they were once again breeding.
“This fish certainly confirms this and we have been able to draw valuable information from it. We will continue to keep an eye on the now increasing population in the hope that it will steadily return to that of 200 years ago.”
Salmon were a common sight on the Derwent, as they were on most of Yorkshire’s rivers, prior to the Industrial Revolution. Since then there have been occasional sightings on the Derwent, with the last adult caught by the Agency during a survey at Stamford Bridge in 1988.
During the summer last year, fishery officers discovered young salmon in Costa Beck and Stamford Bridge, pointing to a return of breeding salmon to the system.
