Ambermouth was an English fishing resort. The Pescadorian was located in Ambermouth, as well as the Ambermouth Seacology Centre.
In 2013, Eldrad's presence caused silicon quartz to grow in Ambermouth harbour. This led to a decline in local fish and bird populations, with puffins, gulls and gannets all falling victim.
The Fifth Doctor and Tegan Jovanka went paddling in the sea at Ambermouth while Nyssa and Turlough explored nearby rock pools.
The silicon quartz infected several residents of Ambermouth, such as Bob Gell and Jim, who were brought under Eldrad's influence.
After Eldrad's ring was destroyed, and both the Eldrad grown from the Watcher and that from the hand killed, the silicon quartz released its hold on Ambermouth and its citizens. (AUDIO: Eldrad Must Die!)