Take a leisurely cruise on the Thames or the Grand Union Canal. Hobbs of Henley operate regular river trips and boat hire along the beautiful Henley Royal Regatta reach. They also offer a series of themed cruises, such as Comedy on Water or the Sunday Lunch Jazz Cruise. Salter's Steamers run scheduled passenger services on the Chilterns section of the Thames, with stops including Wallingford, Goring, Reading, Henley and Marlow.
Hire a self drive launch, a rowing boat or hire a traditional boat with skipper. The website of the riverside Compleat Angler Hotel at Marlow has a good résumé of options on the river from Henley to Windsor. You can also hire a boat and picnic at The Swan at Streatley and The Beetle & Wedge at Moulsford.
Paddle your own Canoe. Longridge, the Olympic Training Centre on the Thames at Marlow, provides an introduction to all sorts of water sports in activity days and short breaks for families with children aged eight and over. There's more activity on the water at Adventure Dolphin at Pangbourne.
The Henley Rowing Association organises a whole range of rowing packages on the famous Henley Regatta course on the River Thames, including half-day sessions for beginners and 'champagne rowing sessions for ladies who lunch'.