The Trust has carried out work on fish since the 1970s when work began on fish populations and other wildlife in lakes created after the extraction of gravel.
Declining wild brown trout populations were researched in the early 1990s to try and halt the declines and successes through habitat management were followed by the River Monnow Project. This project aimed to rejuvinate a neglected and damaged river and benefit the local community. The habitat restoration was carried out on a landscape scale and was the largest ever river habitat restoration project.
The Trust took over the East Stoke Salmon & Trout Research Centre on the Frome in Dorset and continued the monitoring of salmon started with the installation of a fish counter at the site in 1973. This series of data makes it one of the most comprehensive records of salmon movements in Europe. The research into the causes of the decline of salmon and how to reverse this decline is of global importance.