The annual draw-off of the tidal Thames up to Teddington Lock is about to begin – and it will run for a longer than normal, running through to Christmas.

The draw-off occurs when Richmond Lock remains open so allowing the river water to flow out with the tides to the mouth of the Thames.

The annual event is designed to allow maintenance of the Lock and the neighbouring sluice and wear once the water has drained away.

At the same time it reveals most of the river bed, creating something of an eery scene as it exposes what normally lurks beneath the water line.

People can take advantage of the draw-off to search for treasures buried in the mud – a pastime dubbed mudlarking, which actually dates back to the 18th Century.

Old coins, clay pipes, jewellery, and pottery are among the treasures revealed, although people need to beware that the river quickly refills once the tide turns.

The draw off, which normally runs for four weeks through November, makes like difficult for houseboats moored along the bank and those people trying to navigate their way from Teddington down the Thames.

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Richmond's 'man of the river', Keith Arthur, a presenter of Tight Lines on Sky Sports and an expert on all things fishing, has revealed that many unusual creatures, including alien invaders from the Far East, live in this stretch of the river.

Because the amount of fresh water coming down the Thames has decreased, and continues to do so, there is more saltwater incursion, making the water brackish.

As a result, it is by no means unusual to come across clumps of bladderwrack, which is the sort of seaweed normally found amid the crashing waves on the beach.

Anything hollow could contain brown shrimps and, as the tide starts to flood from the very lowest point, postage-stamp sized flounder — flatfish similar to plaice — can be seen swimming in the shallowest water, foraging for food.

As for freshwater species, It's possible to find both duck and painters mussels. The former grows, up to 10-12cm while the smaller painters have paler, concentric rings around the shell.

There are also invasive species, such as Asian clams, Quagga mussels and Chinese mitten crabs.

One year, Keith collected a host of ancient Hornby and Clarke milk bottles. There was also a sign for an old ferry by Eel Pie island, which advertised the fact people could use the ferry to make a connection to 'Southern Trains' to London for a train fare of 5 old pennies (25p) return.

The Port of London Authority said the draw-off will run from Monday, October 31 through to December 23.

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It said: "In order to carry out essential maintenance works and additional repairs on Richmond lock, weirs and sluices, it will be necessary to lift the weirs at Richmond for a period of 8 weeks.

"This will allow the river between Richmond Lock and Teddington Lock to drain down at low water on each tide."

The PLA warned: "During this period river users are reminded that the river will NOT be maintained at the nominal

level of 1.72m … and it is expected the riverbed will be exposed at low water.

"Owners of vessels and structures usually moored between Richmond Lock and Teddington Lock should act in good time, either to move their boats to more suitable moorings or to assure themselves that the boat is capable of taking the ground. Short term moorings are of limited availability in the upper district.

"Vessels navigating through the weirs and upriver of Richmond Lock must do so with great care and with regard to people working in and around the Lock and weirs.

"Persons in charge of vessels are reminded to be aware of their wash, as vessels and structures may be grounding during the low water."