Fly fishing can be done in both fresh and salt water. As well there is a difference between cold water and warm water fishing. According to Wikipedia, in England where water temperatures remain the same for the most part, they call this sport, game fishing which means they are fishing for trout or salmon.

A new fly fishing book by fisheries scientist and avid fly fisher Dr. Robert Sousa helps simplify the process of finding and catching fish. The book, entitled "The 24 Greatest Flies You Don’t Leave Home Without", offers tips on fly selection while discussing where feeding fish are likely to be found.

The choice of a knot for attaching a tippet to a leader can be completely different for the freshwater fly fishing enthusiast to that selected by the saltwater fly fishing enthusiast. Line classes and thicknesses will play a crucial role in knot selection. I do urge both parties not to consider the ‘Multi Overhand Knot’ commonly, incorrectly referred to by many fly fishermen as the ‘Surgeons Knot’. It is a poor selection, fraught with danger, both through slippage and reduction of line strength.