A leaked memo has sparked health and safety fears after revealing that a “significant concentration of formaldehyde” has entered a Welsh river. The internal document from Natural Resources Wales (NRW), which North Wales Live has seen, highlights serious concerns for staff tasked with work near the affected area.

The alert follows the discovery of numerous dead fish in the River Alyn, a consequence of a severe blaze at the Synthite chemical plant in Mold on Tuesday afternoon. NRW is currently probing both the fish fatalities and the broader environmental repercussions of the fire.

In response to the incident, NRW advised the public on Wednesday to steer clear of the river and to prevent animals from coming into contact with the water. Reports emerged yesterday of locals encountering deceased fish and other wildlife along the river, which feeds into the larger River Dee, supplying drinking water to almost three million individuals.