Hi Postie
it doesn't look like a typical Graig Lwyd type VII axe it's too elongated and the rounded face doesn't quite fit. However there are stone implements that do roughly fit this shape and a stone axe deposited in water could be significant. A couple of profile shots of the stone would be useful, is there any trace of a blade?
I would suggest that you take it along to your local museum or friendly archeo for a more informed opinion.
If you are interested in stone axes I can recommend
Stone axe studies: archaeological, petrological, experimental and ethnographic
T H McK Clough and W A Cummins (Editors)
it's available on-line at
http://ads.ahds.ac.uk/catalogue/library/cba/rr23.cfm
with volume 2 here
http://ads.ahds.ac.uk/catalogue/library/cba/rr67.cfm

Be prepared to be told that it's just water-eroded stone though. I could fill a skip with stones that resemble implements from my beach.
cheers
fitz