Where I am in London nearly every park pond or lake has some terrapins, these are the red-eared species and have been thrown in by people who had them as pets and then couldn't handle them as they grew bigger and capable of inflicting a wound.
THE BACKGROUND TO RED EARED TERRAPINS IN BRITAIN
I just wonder if this has been a problem in Accrington/Hynburn area!
These terrapins have been removed in some ponds but they can't get them all, as they are very quick if they sense a threat. They are a threat to natural wildlife!