When Dr Dempsey looks at the developed prints in the darkroom chemical tray he shows shock when the final print clearly shows the head of the Loch Ness monster. He should not have been shocked at that time as he would have most likely seen the monster's head on the negative and certainly when he focused the negative onto the photographic paper during the printing process.
In the outdoor village scenes seaweed can be clearly seen, this indicates that they were shot next to tidal sea water. Loch Ness is a fresh water loch and hence has no seaweed.