Documentary on the wildlife found through the four seasons in the estuary of the River Ythan in north-east Scotland, a five-mile stretch of marshes, mud flats and sand banks situated some ten miles north of Aberdeen. The waters of the estuary are home to waders, wildfowl, shellfish, small crustaceans, fish and otters. The estuary is a nature reserve and, since the 1950s, the University of Aberdeen has been running a research project to examine its complex ecosystem.