Staff raced to move valuable items to higher ground as water threatened to flood into the Longridge activity centre in Bisham this week.
The sailing and kayaking areas of the site were submerged and a campsite was left under water as the River Thames reached the centre's boathouse and began to seep into its cafe.
Longridge chief executive Amanda Foister estimated about 50 per cent of the site was flooded by Monday as waters continued to slowly rise yesterday and today.
Staff fear a repeat of the floods of 2003, which caused damage costing about £150,000 to repair, if water rises much further over the next few days.
The Quarry Wood Road centre, which cannot get insurance, is now giving serious consideration to investing in a new flood defence measure.
The system, which would cost about £10,000, would involve an inflatable dam-style defence barrier to keep water at bay and the charity has appealed for donors to help cover the cost.
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