A murder investigation has been launched following the discovery of a body in the River Severn outside Llanidloes on Sunday.
The body of a 34-year-old woman was discovered at around 4pm on 28 May.
A 46-year-old man was arrested on suspicion of murder by officers later that day.
He remains in police custody, Dyfed-Powys Police said.
A spokesperson said that officers are keen to speak to anyone who may have witnessed, or has dashcam footage of, a man and a woman in Llanidloes, or on the A470 between Llanidloes and Dolwen, on Saturday or Sunday.
"The woman is described as white, 5ft 4ins, of small build, with very long dreadlocks, which were past her waist," the spokesperson added.
"She was wearing a grey coloured top, dark trousers and white trainers.
"The man is described as white, approximately 6ft, of stocky build with dreadlocks in his hair and a dark coloured bandana.
"He was wearing a short sleeve, high vis-style jacket, T-shirt, shorts and light-coloured trainers, and was in possession of a black style bag with a single strap.
"He had a small, dark-coloured dog with him.
"We would also like to speak to the person who gave the man and his dog a lift between Welshpool and Shrewsbury, dropping him off near the Dinky’s Dinahs layby on Sunday.
Officers are "not currently looking for anyone else in connection with this matter," the Dyfed-Powys Police spokesperson added.