How is the glide ratio affected when converting a wheeled plane to floats? I'm looking for published data that describe the effect on glide ratio when an aircraft is converted from wheeled to float configuration.  I suspect that the glide ratio goes down considerably due to all the drag from the floats and attachments, but an internet search turned up nothing.

I'm particularly interested in DeHaviland Beavers and Otters (which commonly have their gear switched between wheels and floats), but any source would be appreciated.
As glide ratio is the same as the L/D ratio, the increase in drag due to the addition of floats will reduce it. The Beaver's POH gives the effect of addition of floats in the glide ratio:



DHC-2 Beaver's Glide ratio; image from DHC-2- Beaver POH

Note that at their configuration for best glide ratio, there is a drop in about 10% in glide ratio for the configuration for floats. This will differ for different configurations and operating conditions, but the basic effect of addition of floats will be a reduction in glide ratio.