Afon Tywi
From Tardis Wiki, the free Doctor Who reference
The Afon Tywi was a river in South Wales.
Following part of the river from east to west, it roughly followed part of the A40, before curving southwards, passing Carmarthen on it west bank. It flowed under the A48 and continued roughly south, passing Llansteffan on its west bank. Two other rivers flowed into it as it continued south, before flowing out into Carmarthen Bay.
The Afon Tywi appeared on Mary Cooper's map of overflow camps in and around Wales. (TV: The Categories of Life)