stucco under water? how will it perform

Dear pond aficionado's,

I'm about to apply some natural stone to my cement block (fiberglass
coated) pond. The rock (approximately 1-2 inches in diameter) will be
tightly layed on the sides and progress to a more sparse distribution
on the floor of the pond. I need to grout the rock but the layout is
too sparse on the floor of the pond so I was thinking of using stucco
as the filler (grout) between my rocks. How does stucco perform
submerged in water?

Thanks for any info you might provide.


Wayne