Some possibiities ...

(1) use a polarizing filter ... properly oriented, this should cut down the glare. 
For an example, please view the message thread with subject,
Obglitory Slow Motion Water, and scroll down to the last 2 messages to
see the discussion and example images. 

(2) form a light tent around the subject -- use parchment paper to form the tent. 

(3) as a last resort, mist the subject (make SURE you have permission)
-- use a spray bottle and distilled water; the mist will break up the reflections. 

This last suggestion is also effective to enhance color saturation -- try that
out on an otherwise dull rock/boulder ... but not in direct sunlight. 

Comments, please. 

--Martin