Officers from the Environment Agency (EA) were at Molesey Lock near Hampton Court Bridge last week, as part of a programme to provide a picture of the nation’s fish populations.

The officers are surveying 70km of the Thames, from Temple in central London to Teddington, as part of the two-week National Fish Monitoring Programme.

They were at the lock on Thursday, September 17, and Friday, September 19, and used a specialised electro-fishing boat to catch an array of fish species.

The vessel has two arms extending from the front of the boat that pass an electric current through the water, attracting and momentarily stunning the fish.

Officers then record the length of the fish and scales are taken to determine the age, before they are safely returned to the water.

The EA said the results of the program would help them work out how factors such as water quality, flows and habitat influence the health of the UK’s rivers.

The EA will also be able to assess the potential impact on the river of developments such as moorings and hydropower schemes.

George Gerring, the agency’s fisheries technical officer, said: “We can learn a great deal about the ecology of our rivers simply from the condition of its fish.

"Fish need a good supply of food and shelter in order to thrive. The information collected in these annual surveys helps us to understand the population structure from year to year and range of fish species living in our rivers.”

More than 5,000 fish, including minnows, pike, carp and eels, have been caught and measured this year and the EA said fisheries staff have been struck by the large number of “specimen” sized fish that they have seen.

These include perch weighing over 3lbs, pike weighing over 24lbs, barbel weighing over 10lbs, very large eels and even a carp which weighed in excess of 37lbs.

Mr Gerring said: “The number of very large fish we have caught this year could be due to a series of years with low flows and warm water temperatures that has caused an abundance of food available.

"These fish are a great indication of how healthy the Thames currently is. It is also great news for any anglers wishing to visit the Thames, as there is every chance they could catch a personal best fish.”