Hundreds of people turned out to challenge a plan by Thames Water to drain millions of litres of water a day from the Thames and replace it with treated effluent.

The scheme has raised concerns about the effects on river life, mostly the impact of the relatively high temperature of the effluent on fish, larvae, insects and plants.

There are also concerns about the effects of the change in the chemical make-up and salinity of the river.

Separately, there are worries the scheme will reduce the level and flow of the river to the point that boats find it difficult to navigate.

The venue for the consultation event at the Old Town Hall, Richmond, was unable to cope with the numbers of people keen to give their views with the result there were queues on to the street.

Richmond Park MP, Sarah Olney, who quizzed Thames Water staff about the scheme, said it 'stinks'. The Twickenham MP, Munira Wilson said the company should concentrate on tackling scandalous pipe leaks, which are losing 635m litres a day.

An early version of the Thames Water scheme was dropped two years ago following objections from the Environment Agency, Historic England and Natural England, as well as river and angling-related organisations, the Port of London Authority, the River Thames Society, the South East and Thames Rivers Trust, and environmental campaign groups.

However, Thames Water has now revived the idea with some changes, most notably reducing the amount of water involved.

The initial proposal included taking up to 150 million litres from the Thames from a site between Teddington and Hampton Court. This would be replaced by an equivalent amount of treated effluent from the Mogden sewage works, which would be pumped into the Thames down river closer to Teddington Weir.

The new scheme would reduce these numbers to around 75 million litres a day, which would be taken at times of drought – most likely in the summer months. There are concerns that even this measure will be harmful, particularly if the Thames is already at low levels because of a drought.

The water taken from the Thames will be transported via a tunnel beneath London to east London. A new 15km pipeline would take treated effluent from Mogden to the Thames near Teddington.

Sarah Olney said: "Franky, the whole thing stinks. Thames Water loses 635 million litres of water a day to leaking pipes. They need to focus on fixing these, rather than filling the river with sewage."

She said regulators such as the Environment Agency and Ofwat do not have the resources to properly police such schemes.

The MP said: "No one wants to live near, swim in or travel on a dirty river. If these plans go ahead, Thames Water needs to be held to the highest possible environmental standards but there is no agency which can ensure these are met.

"The Conservatives have gutted any agency that can hold water companies to account. They have left Ofwat toothless and slashed the budget of the Environment Agency repeatedly, proving they simply do not care about keeping our rivers clean."

Munira Wilson, who was speaking in Parliament when the event took place, sent along a member of staff on a fact finding mission.

She said: "My concerns is that these proposals were previously thrown out by the Environment Agency and we know that Thames Water are regularly pumping raw sewage into the Thames at Mogden, and so I think there is a real concern about trust.

'The proposal was previously ruled out because of concerns about the ecosystem and the ecology in the water.'

The company said it is currently carrying out a 'high level' consultation at the moment before coming up with more detailed proposals. It has argued that the Teddington and Mogden scheme is the quickest and cheapest way to combat the effect of droughts and ensure there is enough tap water in the future.