Around 70 tourists connected a stream vessel successful Peru person been detained by an indigenous radical arsenic portion of a protestation against a caller lipid spill.
The UK Foreign Office says a "very tiny number" of British nationals - believed to beryllium 3 - are connected the boat.
Peruvian, Swiss, American, Spanish and French nationals are besides believed to beryllium connected board.
One British passenger, Charlotte Wiltshire, said the radical was starting to tally retired of nutrient and water.
"Conditions are starting to deteriorate," she said successful a connection sent to the BBC.
She has asked for an "intervention to get america retired of here", saying determination were pregnant, diabetic, aged and sick radical connected the boat.
The tourists are not thought to person been harmed. They person been held since Thursday morning.
Activists from the Cuninico assemblage released a connection earlier successful the week saying that from midnight connected 1 November, nary boats oregon vessels would beryllium capable to pass.
"We request that the authorities talks to the Cuninico assemblage oregon look consequences - the eventual work lies with the President of the Republic [Pedro del Castillo]", the connection read.
Speaking to a section TV station, Prime Minister Anibal Torres appeared to blasted the Cuninico assemblage itself for cutting the pipeline.
The assemblage refused to enactment astatine a gathering with a delegation sent by Peru's premier curate connected Friday, it has been claimed.
One Peruvian rider connected the boat, Regina Mortua, said they were stranded astatine the rima of the Cuninico River.
"A fewer minutes agone the autochthonal assemblage decided to instrumentality our [tourist] vessel adjacent to their town," she said.
"A fewer hours agone different vessel came for america to board, nevertheless it was not possible, due to the fact that it lone transports food...
"They person conscionable informed america that perchance astatine nighttime they volition transportation each the passengers successful boats. However, nary rider wants to permission their belongings."
Another tourer told section TV the radical had been fed, but had been told they would beryllium held for up to 8 days, if determination was nary resolution.
The UK Foreign Office said: "We are successful interaction with the section authorities and a precise tiny fig of British nationals progressive successful an incidental successful Peru."
The lipid spill that sparked the protestation from Cuninico's indigenous assemblage happened connected 16 September, and protests began aboriginal that month.