Officers from Natural Resources Wales have identified the cause of an oil spill, which let 3,500 litres of oil into a river near Crickhowell on Thursday.
The cause of the spill has been traced to a disused oil tank.
The incident has already had a significant impact on the stream, killing many fish and affecting people's gardens.
An investigation is taking place after an oil spill which has polluted approximately 850 metres of river in Crickhowell.
An estimated 3,500 litres of oil has escaped into the river, and the surrounding area, also affecting nearby gardens.
Officers at Natural Resources Wales say they're making efforts to prevent more oil reaching the river, but the impacts are already evident.
Many people called to report the incident earlier today, which is causing an oily sheen on top of the water and a strong odour.
The source of the pollution has been identified, but the oil has now worked its way downstream, affecting the main River Usk.
In tonight's episode:
Carl joins History Chef Ceri Lane at Tretower Court and Castle near Crickhowell.
They'll be making 'hardtack' biscuits, a snack historically eaten by sailors, when they were at sea for months on end.
Carl will also be finding out about the site's rich history, from its time as a grand country house, through to its use as a farm, and eventually its restoration.
Also in tonight's episode:
Andrew Price will be at mountain biking centre Bike Park Wales in Merthyr Tydfil.
Ruth will be exploring the Pembrokeshire Coast, and Hannah is on Saint Catherine's Island in Tenby.
Phillip Stocker's daughter, Charlotte from Abertillery, is stranded in New York after attending her friend's wedding.
Members of a wedding party from Wales who are stranded in New York due to Hurricane Sandy have told ITV Wales their airline has informed them they won't be able to return to the UK until at least Saturday.
Around 30 guests had flown out to America to celebrate the couple's big day but many have since been unable to fly home as flights out of New York have been cancelled.
Some have also had difficulties booking hotels and nine guests have been forced to share one room.
More than 200 Welsh school children and a 30 strong wedding party are among those trapped in New York tonight as the city faces a potentially deadly storm surge.
They are among thousands of British tourists being forced to seek shelter as flights to and from the East coast of America are cancelled and thousands of Americans are having to evacuate their homes.
Pupils from Carmarthen who have arrived in New York today, just as the city prepares for hurricane Sandy, are 'safe and secure' according to the school.
Pupils and staff from Ysgol Gyfun Bro Myrddin have been in America since last week and have already visited Washington D.C and Philadelphia.
As forecasters predict strong winds, heavy rain and flooding the school say they are in constant contact with the party and they are keen to reassure parents, relatives and friends that the group are safe and secure