A large number of fish died in the River Colne due to low oxygen levels, an investigation has found.

The Environment Agency (EA) has received the results of its tests following the incident towards the end of August.

A resident had been walking through Oxhey Park when he found the fish in the river and raised the issue.

The EA said its officers had attended the site and “confirmed a large scale fish mortality incident of multiple species including roach, bullhead, minnow and chub of varying sizes”.

Officers also took water samples from the site and the results have now come back.

The EA says water quality readings taken from the river indicated there was no pollution.

But it said that due to a dry spell of weather, followed by rainfall, the river experienced a temporary reduction in oxygen.

"As a result of low oxygen levels in the water, there were fish deaths," a spokesperson said.

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

The council said it worked with the EA 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”.

Cllr Tim Williams, cabinet member for client services and sustainability, said it was “deeply upsetting" to hear that fish had died.

He added: “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."