He said he was "bitterly disappointed" by the pollution, which has caused an "enormous problem" in the area, but admitted he had not spoken to any local businesses about the spill when visiting the area.
Senator Farnham said: "It couldn't have come at a worst time.
"We're just waiting now to find out what action can be taken and what we can do from an environmental point of view to get it cleared up as quickly as possible."
He said the current big tides would help speed up the process.
"We must get to the bottom of how and why it happened," he added.
Slurry spill 'could lead to a shortage in water supplies'
A valley polluted by a spill of animal waste is a key water catchment area for the island, and the spill could lead to a shortage in supplies in the hottest part of the year, Jersey Water says.