Well, not recently! However it’s true that Fleet Pond was used for the testing of hydroplanes by Geoffrey de Havilland and his log book records several flights from April 1912.
At this time, de Havilland was working as a test pilot and designer at the (then) Balloon Factory at Farnborough. This later became the Royal Aircraft Establishment.
Recently (July 2008) a book has been published on The Balloon Factory by Alexander Frater and reviewed here. If anyone has a copy and has found any further information on the role of Fleet Pond, please let us know (via a comment below)!