Experts have warned that houseboat owners emptying raw sewage into a river could cause an "environmental catastrophe".

A series of vessels lined up along the mudflats on the River Adur in Shoreham are pumping out gallons of effluent, according to a council report.

Only one of the houseboats to the south of the Norfolk Bridge is connected to the mains sewer, meaning the rest are discharging untreated sewage directly into the river, which is popular among boaters and canoeists.

Fish, birds and other wildlife could all suffer substantial damage because of the sewage and any human coming into contact with it could face serious illness.

The true extent of the problem only came to light after Adur District Council compiled a report on "good practice" for the houseboat residents.

District council leader Neil Parkin said: "Having raw sewage in the river in the 21st century is unacceptable and we must work together to get this sorted.

"We have written to all the agencies concerned and plan to meet up soon to see how we can collectively use our powers and responsibilities to solve this problem."

Exact levels of contamination in the river are still being assessed but experts have already said that levels of pollutants rise on an incoming tide.

The council, along with Southern Water and the Environment Agency, all plan to tackle the problem and at least find an alternative method of disposing of the sewage, which could include connection to the mains.

A Southern Water spokeswoman said: "If the houseboat owners request to be connected to the public sewer network then Southern Water would help with this if it were practical and economically feasible.

"The owners also have the option to employ private tankers to take the sewage away for them if they needed to."

An Environment Agency spokesman said: "We will be working with the council to try to establish a solution to this problem. It is unacceptable to have pollution of this type."

There are around 25 houseboats on the section of the river, including the controversial former Germanbuilt Nato minesweeper Fische, which was the subject of a long-running wrangle over its length in 2005.

One owner, who did not want to be named, said: "I can understand why they might think it's a problem but we live on boats and by definition we're not connected with the sewerage pipes. I would think most would be willing to connect."