Bailiffs moved in to evict campaigners from a house at Thrupp Lake in Radley, near Abingdon, before dawn yesterday.
A group of seven campaigners - four women and three men - took over Sandles House, by the side of the lake, in protest at plans by power giant RWE npower to dump ash from Didcot Power Station in it.
Npower was given a possession and eviction order at Oxford Crown Court on January 24 - but protesters were defiant that their campaign was not over.
The eviction began at around 5.30am. Squatter Lisa Peakman, 38, said: "I was woken by a loud bang and showered with broken glass from the French windows. The bailiffs were dressed in black and wore black balaclavas. There was no warning, they just smashed their way in."
More than a dozen bailiffs carried out a search of the five-bedroom property and ordered the seven squatters to leave the house.
One protester locked himself on to a concrete-filled oil barrel in a small cabin on top of a 35ft scaffold structure built by the squatters at the side of the house.
It took bailiffs nearly two hours to release him and the tower was then demolished.
Another squatter Dave said: "We may have lost round one, but we will re-group and consider our next course of action."
The Rev Malcolm Carroll, who is acting as a spokesman for the protesters, said: "We have planned for this, but it is still a terrible thing to see the bailiffs, supported by police, arrive.
"But our campaign is planned in phases, and this is just the first of them."
A member of action group Save Radley Lakes, Dr Peter Harbour, one of eight observers at the site, said: "The squatters have put up a brave fight against a powerful company, whose plans to use Thrupp lake as a dumping ground for fuel ash is to be condemned."
Npower spokesman Kelly Brown said: "The team of bailiffs working on behalf of RWE npower went in and removed most of the squatters, apart from one who had attached himself to a tower and, for health and safety reasons, we waited until it was safe to remove him."
Operations manager at the power station, John Rainford, said: "Our proposals have been developed with the full support of independent ecologists who will monitor all activity at Radley and ensure that every care is taken to protect the wildlife on the site."
Police arrested one protester, who was taken to Abingdon Police Station.
* Solicitors acting for Save Radley Lakes have written to npower to say work should not start until an application to register the lake as part of a 'Town Green' has been decided.
They warned the group might seek an injunction if work started before the application was decided.