Is this the first time you have had it in the sunlight?  I had some white specks from sanding, managed to get rid of most of them by a good whipe down with paint thinner.  Do they still show up when the boat is warm?  are they visible when you first went outside (and the boat had not had time to adjust to the temp).  I have not had my WD out in freezing weather yet, but the epoxy/varnish work on my SOF did not show any changes in sub freezing weather last season.

How long ago was it buiilt? Is all of the epoxy covered with varnish or paint? Any chance it is unprotected epoxy starting to break down due to UV exposure?

WD12 was built 1 month ago. I did not carnish, yet. springtime when I can do it outdoors.

All 4 trips to the pond were just after sunrise. So maybe a toal of 8hours exposed to any sunlight. Also frshwater not saltwater. 

I will check tonight to see if white specs are still there.

Thanks!

I suspect that what you are seeing is the wax (amine blush) that is reacting to the water. Remember, wax rises to the surface of many epoxies to aid in surface cure, and must be removed before re-coat or application of finish.

Wash well with soap and warm water. Might take a bit of scrubbing with a green (scotchbrite) kitchen scrubber. You might also use wax and grease remover available from any automotive paint store prior to the washing step.

 This, of course, is assuming that your epoxy was properly proportioned and mixed and that the project did not get cold (below 40 degrees) during cure. Some epoxies suffer from "cold cure inhibit" meaning that if allowed to chill during cure, may not fully cure, ever.

What type of epoxy did you use?  Sure sounds like Amine Blush to me