Police investigating after allegation incident took place at Sandy Water Park in Llanelli.
It was reported to them at around midnight this morning.
A 24-year-old man has been arrested on suspicion of raping a woman, and remains in police custody at this time.
Police would like to reassure the public that they are treating this as an isolated incident and are not looking for anyone else at this time.
Anyone who was in the area after 6pm last night is urged to contact police by calling 101.
If you are deaf, hard of hearing or speech impaired text the non-emergency number on 07811 311 908.
Quote reference: DP-20190328-001