Nature lovers have been asked to help track the "kings of the canals" on west London's waterways.

Herons earned the regal epithet thanks to their place atop the food chain, making them a great barometer of the health of the ecosystems upon which they rely.

The Canal & River Trust wants your help to monitor their numbers on our waterways as part of the Great Nature Watch, a nationwide survey of wildlife.

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The charity is particularly keen for people to report sightings along the Grand Union Canal , stretching from the Thames at Brentford all the way to Birmingham.

It says grey herons feast largely on fish, frogs and small mammals, meaning poor water quality can lead to a rapid depletion in their numbers.

'Herons even gobble up the odd duckling'

Dr Mark Robinson, ecologist at the Canal & River Trust, said: "As adult birds face no natural predators, they're the kings of the canals, and take their pick of fish, amphibians and small mammals around the waterways, even gobbling up the odd duckling.

"Large numbers of herons usually mean healthy, thriving canals and rivers, as they're natural barometers of water quality, fish stocks and much more – even down to the insect and invertebrate populations that feed their prey.

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"Equally, if there are areas without many sightings, we can have a look into if there are any reasons they might be being put off."

The charity says the UK is believed to be home to around 13,000 breeding pairs of herons, and their numbers are understood to be increasing.

You can submit sightings by downloading the charity's free mobile app "eNaturewatch", which is available via the Apple App Store or Google Play Store.