The section of the Thames between Teddington Lock and Richmond Weir will undergo a dramatic change this week.

That is because Richmond Weir is being lifted from this morning.

This is to pave the way for the lock, weirs and sluices to be inspected and repaired.

Weirs regulate the water level and lifting it will cause the river to fall to its natural level - which is remarkably lower than many might expect.

River Thames custodians the Port of London Authority explained exactly what will happen in a very detailed post which you can read below.

"One of the roles of Richmond Lock and Weir is to maintain the river level between it and Teddington Lock at of 1.72m above sea level, which is enshrined in an Act of Parliament. Sea level in Great Britain is calculated in reference to Ordnance Datum Newlyn, which was the Mean Sea Level at Newlyn in Cornwall between 1915 and 1921.

"Without the weirs in place, the river will fall to its natural level, which exposes far more foreshore and makes navigation at low tide very difficult.

"Owners of boats and structures usually moored between Richmond Lock and Teddington Lock should take action 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.

"River works licence holders and riparian landowners are reminded that any interference with the foreshore such as dredging, excavating or disturbing the riverbed requires a licence from the Port of London Authority.

Environmental legislation provides for very high levels of fines when licensing requirements are not strictly adhered to."

The draw-off provides the opportunity for maintenance of the lock and weir because much of their structure and mechanics are exposed for a much longer period of time.

Richmond Lock and Weir manager Jim Deeney said: "It shows people what the lock and weir does and allows everyone to see parts of the river that are not normally visible.

"One year we discovered a car that had been driven into the river, which was not visible when the river was at its maintained depth."

The draw-off started at 9.45am this morning. It will end at 2.50pm on Friday, November 27.