The debris is thought to be washing down from flooded areas upstream, including Welney Wash, where high water levels caused by the recent heavy rain are washing down vegetation.

Gail Kingston, who operates the ferry service with husband Steve, said the build-up had been so bad that at one point the boat's propellers were getting clogged on each journey across the river.

Mrs Kingston said: "Without the new boats with outboard engines we would not have been able to run the ferry. Luckily we are able to lift the engines and clear out the propellers by hand.

"We also have to keep manually clearing the jetty and the steps so they are safe to use. It all takes time."

Not only is more debris being washed down the river every day, but material washed out to sea has been returning on the tide, adding to the problems.

Mrs Kingston added: "The situation is worse on the West Lynn side of the river, where it goes round and round on the eddy near the steps. We're coming up to eight years here and we have never seen anything like it."

Lynn harbour master Mr John Lorking said: "Quite large rafts of weeds are coming down the river as a result of inland flooding.

"As the water is rising it's bringing vegetation down from the fields which are being flooded. In the summer we have had occasions when we have had a high tide and straw has come down the river."

He went on: "It's a problem we are aware of, but because of the flooding upstream it can't be avoided. I would imagine we would see the water levels decreasing in the coming week or so as water levels fall upstream, provided we don't get any further prolonged periods of rain."

A spokesman for the Environment Agency said any debris washing downstream was not its responsibility once it entered areas outside its control, such as the South Quay, which is the responsibility of Lynn Port Authority.