The grisly discovery was made on a farm near the local aerodrome.
Speaking to Lusa News Agency, a source from the area’s fire brigade said the fire station had been contacted by the police just after midday to drain water from a tank on the site.
“We removed the water and found the bodies of the three women, one of whom was pregnant, and they were removed”, Pedro Araújo said.
Portuguese police began investigating the case following a tip-off from Interpol.
Ongoing investigative work with Brazilian authorities is said to have led to last Friday’s discovery.
According to reports, the women were first reported missing back in February this year and PJ police had allegedly already previously combed the area in question in March or April.
The police said “the alleged perpetrator was back in Brazil and his detention led to the location of the bodies.”
An employee of the veterinary hospital is also involved in the case.
The bodies of the women, two of whom were sisters, were due to be autopsied on Tuesday.
Newspaper Jornal de Notícias reported that the alleged perpetrator is a Brazilian citizen named Dinai Alves Mendes, who they claim has confessed to the triple murder.
The report identified the three victims as Michelle Santana Ferreira (28), her sister Lidiana Neves Santana (16) and a friend, Thayane Mendes Dias (21).
The suspect worked at an ‘animal hotel’ operating on the farm where the bodies were found.
Newspaper Correio da Manhã indicates the alleged murders may have taken place to cover-up for an illegitimate affair, as Michelle, who is said to have been romantically involved with Dinai, was reportedly unaware he was still married to a woman in Brazil.
The newspaper claims Michelle was involved with Dinai and three months pregnant when the main suspect’s wife was due to travel from Brazil to Portugal.
The suspect is understood to have shared a house with the three women.