A porpoise appeared to get stuck in the Thames near Gravesend on Friday with experts blaming the increased use of sonar technology.
Gravesham Tourism tweeted a picture of the mammal with rare breeds specialist Wayne May believes it to be a female porpoise.
The 42-year-old told News Shopper: "I’ve done a lot of research and basically they are getting confused.
"It’s definitely increased - I got called out 12 times last year for porpoises and only five times the year before.
"People often think they are dolphins but then they turn out to be porpoises.
"They use underwater signals to detect their prey - things like sea bass - and so when military use sonar, these animals get disorientated.
"The more we use echo technology at sea, this does affect their marine environment."
Mr May explained how porpoises are very commonly spotted but he believes rarer creatures are also being baffled by the increased use of technology.
He said: "It is mainly the whales and the dolphins who I think are getting more confused by this technology.
"They can end up dying because they can’t survive around here, there isn’t enough of their food sources.
"There is not a lot you can do. Often whales end up getting washed up on the shore and dying.
"We had a whale which came through Gravesend a few years ago and it died as it was being transported back to London."
Mr May has worked with animals for more than 20 years and runs a sanctuary in London Road, Dartford.
Sightings across the News Shopper patch
- In June last year Punters in the Sir John Franklin pub in Greenhithe High Street were shocked to discover a porpoise washed up next to a pub.
The dead animal was spotted on the steps to the pub which looks out onto the River Thames.
- A family walking along the Thames were shocked to spot a seal in the water off Morden Wharf in Greenwich in January last year. A month later, video footage revealed the animal playing with the family’s pet dog.
- In September 2009 a 28ft young humpback whale was found near the Dartford Crossing and was the first time one has been discovered in the Thames. It is believed to have died from starvation.
- An 18ft northern bottlenose whale was spotted in the Thames in January 2006. It died off Gravesend as rescuers transported it on a barge towards deeper water in the Thames Estuary.