Two dolphins have reportedly been found dead on the banks of the Thames in London, after one was spotted in the river last week.

The common dolphin was seen multiple times from late morning on Thursday, and was described as appearing to be “struggling with the tide”.

But on Monday a dolphin was pictured dead on the bank of the river near Chelsea Harbour Pier.

Another dolphin was found on the riverbank at Greenwich but it is not known when it had died, according to BBC News.

A Port of London Authority spokesperson told the PA news agency: “We are aware of reports of two dolphins that sadly died. We are working with the Cetaceans Stranding Investigation Programme and will recover the animals.”

The British Divers Marine Life Rescue (BDMLR), which was tracking the dolphin on Thursday, was contacted for comment.

On Friday, Julia Cable, operations director at the BDMLR, said: “(The dolphin) was still in the area throughout the evening but its behaviour wasn’t really changing so we didn’t continue monitoring it too late.

“It’s too far really for a dolphin to be up the river.

“It wasn’t really moving very far, it did appear to be struggling with the tide.”

Mary Tester, Thames area co-ordinator with the BDMLR, told BBC London there were a “lot of different theories” on why dolphins were “coming down the river”.

One explanation, she said, was the improved water quality of the Thames over recent years, which had increased the level of fish that dolphins preyed on.

Members of the public who spot a dolphin swimming in the Thames, or any inland waterway, have been urged to alert the BDMLR and avoid following it in boats or canoes.