The Beale Park Thames Boat Show on the river near Pangbourne is a great event located on a private lake with access to the river. There are lots of boat-related exhibitors including boatbuilders and boat societies such as the Thames Traditional Boat Association, many of whom offer sailing and rowing on the lake. Other attractions include a food and crafts tent and a classic car display.
Graham and I are going, starting early and getting back late afternoon. If anyone else would like a seat in my car, post here!
More about the show here:
http://www.bealeparkboatandoutdoorshow.co.uk