An investigation is underway after a large number of fish were found dead in the River Colne in Watford.

The fish were found by a resident walking through Oxhey Park on Monday morning.

The Environment Agency says its officers attended the site on Monday and “confirmed a large scale fish mortality incident of multiple species including roach, bullhead, minnow and chub of varying sizes”.

“There were no obvious signs of pollution, however, we have taken samples and are now awaiting the results,” a spokesperson said.

The resident who found the dead fish alerted West Watford county councillor Nigel Bell to them, who informed Watford Borough Council about it on Monday evening.

Cllr Bell raised health and safety concerns mentioned by the resident, such as children playing near the site and people walking their pets there.

The council is currently working with the Environment Agency to find out what happened, adding that “protecting the fish and all the other creatures that live in and around the Colne and Gade riverbanks is hugely important to us”.

Whilst an investigation is being carried out, the council is urging people to keep themselves and pets away from the water as a precautionary measure.

Cllr Tim Williams, cabinet member for client services and sustainability, added it is “deeply upsetting to hear of these reports of dead fish”.

He said: “Protecting the fish and all the other creatures that live in and around the Colne and Gade riverbanks is hugely important to us, so we will work with the Environment Agency to find out what has happened.

“As a precautionary measure, we advise people and their pets to stay away from the water until the cause of the event has been determined.

“We have just started a ten year project to renovate the Watford section of the River Colne that will involve an extensive clean-up, and a key goal of this is to attract back the original biodiversity of the river and its banks including plants, fish, birds and insects."