Hi Charlotte,
just done a quicky on this and took 30 seconds with DCE tools using Perspective. Its an Adobe compatible Plug-in and costs about £18. One nice point on this plug-in is that the picture you are "Perspecting" has a grid of squares superimposed on it and the added bonus is the points can be taken outside of the original picture,it also has a live preview. As the other post has mentioned you loose the sides of the picture but yours had plenty of "spare" to crop .You can download a free trial, just go to Google and type DCE Tools..
Regards Brian
P.S just gave a bit of Gamma adjustment as well to bring up the water reflections a bit