Sharks have been found in the River Thames in Kent – but there is no need to panic.

Dogfish, a type of small shark, have been found in the River Thames at Denton, Gravesend, during the 50th City of London Thames Fishery Research Experiment.

The research takes the form of an annual fishing competition, first held in 1972.

Four dogfish were caught this year, even though just one had been netted during the contest in the previous 49 years.

The results are vital for organisations such as the Environment Agency and Port of London Authority to assess the state of wildlife in the Thames based on the variety, number and size of fish species caught.

The competition includes more than 80 anglers on the foreshore of the Thames at Denton, Gravesend, who catch, record and return the fish to the water.

The City of London Corporation said: "Over the years, the experiment has proven that the Thames remains the cleanest river in Northern Europe."

The results of this year's event, released on November 29, said: "With only one dogfish caught over the previous 49 years, it was a welcome surprise to record four, including a specimen of 56 centimetres.

"Dogfish are plentiful in the estuary but not so common in the middle reaches.

"This is further evidence of positive change in water quality within the River Thames."

As one of the longest running citizen science projects, this year's event also saw the highest number of fish caught since 2005 and the most species found since 2008.

In the early 1970s when the event was founded, only whiting, eels, flounder and sole were found, but today there is an average of 7.5 different species recorded every year, and this year, nine species were found.

After two years of reduced-scale events due to the pandemic, the experiment returned to its usual format for its 50th anniversary this year.

Chairman of the City of London Corporation’s Port Health and Environmental Services Committee Keith Bottomley said: “The Thames Fishery Research Experiment tracks the number and variety of species recorded over time.

"For 50 years, the results have provided consistent, comparable data which are analysed to highlight improvements in the river’s health.

“The results show a clear link between a clean, healthy river, and the diversity of species that live in it. It also highlights the connection between efficient pollution controls and better biodiversity.”

The founder of the fishing research experiment, 88-year-old Reg Butcher, was awarded with a British Empire Medal earlier this year for 50 years of voluntary service.

He has been largely credited for the Thames' current status as one of the world's cleanest rivers, just 60 years after it was labelled as 'biologically dead'.