Six people went into the water near Wheatley’s Eyot just before 9 o’clock this morning.
The Fire Brigade says five people have been safely located but a sixth is missing.
The stretch of river is popular with river users but it is extremely fast flowing.
People are being advised to avoid the area.
Surrey Police statement;
We, along with other emergency services including SECAMB and Surrey Fire and Rescue, are currently on scene at Sunbury Lock near Wheatleys Eyot after we were called at around 8.50am this morning (11 October) following reports of a small boat capsizing.
We believe that there were six people involved in the incident, and five of these have been safely located.
We are working to locate the outstanding person and will update you as soon as we have more information.
Please avoid the area if possible.
