A coordinated effort involving the Port of London Authority and British Divers Marine Life Rescue successfully guided a pod of 27 pilot whales out of the Thames estuary and back into the North Sea over the weekend, after the marine mammals became stranded in the shallow waters near London.

The pilot whales, each approximately five meters in length, were first spotted on Thursday afternoon near Gravesend, prompting concern among authorities due to the risk of stranding in one of the UK’s busiest waterways. Although the whales initially appeared to return to deeper waters on Thursday evening, they were observed moving upriver again the following morning.

Lyn Kindlen, harbour master at the Port of London Authority, took charge of the unusual rescue operation on Saturday. Partnering with the British Divers Marine Life Rescue (BDMLR), Kindlen organised a fleet of eight boats forming a U-shaped formation to herd the pod toward deeper waters. The operation, described by Kindlen as one of the most memorable of her career, involved a six-hour careful maneuver starting near London Gateway, a port located on the north bank of the Thames at Thurrock.

“The whales were confused and moving in multiple directions,” Kindlen explained. The team had to proceed patiently, frequently pausing to reassess the pod’s movement and adjust the approach while balancing heavy commercial vessel traffic on the river.

The boats guided the whales over a distance of 23 miles, including stops to allow the animals to rest, until reaching Redsand Towers — a group of Second World War-era fortifications situated on stilts in the estuary. After passing Southend Pier, the whales began swimming steadily toward the North Sea, prompting relief among the rescue team.

Despite the success in saving 25 whales, two individuals from the pod were found washed ashore deceased on Friday. BDMLR volunteers suggested that the pod’s venture into the Thames might have been motivated by a search for herring or confusion caused by the loss of the pod’s matriarch, who was among the whales that died.

Pilot whales are native to the North Sea but are infrequently seen this far upriver due to the river’s shallow depth. Experts note that pilot whales often strand themselves when they cluster tightly in response to perceived threats or stress, including noise pollution.

Meanwhile, an unrelated stranding of a larger pod occurred off the coast of Northumberland on Sunday, where six pilot whales were found dead after a group of 40 swam close to shore.

Three days after the Thames incident, no signs of the original pod have been observed by Port of London operators. Kindlen expressed cautious optimism about the outcome. “At the start, we feared this could have a very sad outcome,” she said. “I’m proud that the Port of London Authority and BDMLR came together to make sure that didn’t happen.”