A woman found murdered 31 years ago in a river in Belgium has been identified over three decades later thanks to her flower tattoo and an international appeal, Interpol said on Tuesday.

The Lyon-based global police organisation said she was Rita Roberts from Cardiff in Wales and British.

Roberts, found lying against a grate in the river Het Groot Schijn in Antwerp on June 3, 1992, had a tattoo of a black flower with green leaves and the inscription "R'Nick" on her right forearm.

She was 31.

"A family member in the United Kingdom recognised the tattoo on the news and notified Interpol and Belgian authorities," Interpol said in a statement.

The breakthrough followed an international appeal on Interpol's Identify Me web page where police share previously confidential information – so called Black Notices – about unsolved cases hoping for input from the public.

The page, launched in May this year, seeks to identify 22 women found dead in recent decades in Germany, Belgium and the Netherlands, Interpol said. Rita Roberts is the first case of the 22 victims to have been identified.

Information volunteered had also brought progress in other cold cases to make progress.

Rita Roberts has been "formally identified" by her family who travelled to Belgium to meet investigators.

"Whilst the news has been difficult to process, we are incredibly grateful to have uncovered what happened to Rita," the family was quoted in the statement as saying.

Police in Durham, England, said they had supported the family, some of whom live in the area, "during what has been a heartbreaking time for them." (AFP)