One of four people held in Mozambique on suspicion of sabotaging the hydro-electric Cahora Bassa dam has said they did not intend to destroy it.
The foreigners are accused of putting a corrosive chemical in the turbines.
"We were throwing into the water what we believe could bring positive energy to the region," Carlos da Silva said.
The wife of another detainee told the BBC the substance was "orgonite". Proponents of orgone energy say it is a life force with healing properties.
In an e-mail to the BBC, Friederike Ritschl said her husband Georg, who is German, and his three companions - from Portugal, South Africa and Botswana - had been held for more than two weeks.
She said they were part of project called Orgonise Africa, which, according to its website, has undertaken "countless orgone healing expeditions" in Africa since 2002.
Portuguese detainee Carlos da Silva told journalists in north-west Songo district that tests so far had revealed nothing "toxic".
"We were arrested by the police on suspicion of terrorism, something we find incredible," he said.
"We came here with good intentions. Maybe we should have contacted the local authorities before," he conceded.
But Deputy Interior Minister Jose Mandra says the four suspects will remain in custody until the investigations have been completed.
He said there were various laboratory tests being conducted to determine how harmful the substances were.
The BBC's Jose Tembe in the capital, Maputo, says Mozambique's president has also commented on the issue, urging caution.
"It's very irresponsible to reach conclusions before the investigations are complete," Armando Guebuza said.
Maputo city lawyers say if it is proven that the substances thrown into the dam are harmful to humans, animals or the dam's infrastructure, the suspects may face sentences of between two and eight years.
Mrs Ritschl said the orgonite was "from clear cast polyester resin" and "aluminium filings".
The dam was built in 1974 under former colonial power Portugal
She said the resin manufacturer had confirmed in writing that the resin was stable in water and "only negligible amounts of styrene could be released, if at all".
"As the aluminium is mostly enclosed in the resin, there is no danger there as well."
The Cahora Bassa dam, on the Zambezi River, is a vital source of electricity for Mozambique, South Africa and Zimbabwe.
Built in 1974 when Mozambique was still a Portuguese territory, ownership of the dam transferred two years ago to the Mozambican government.
Mozambique is among African countries which have pledged to provide electricity to South Africa during next year's World Cup to prevent power cuts.