The river is rich in insect life, and in excess of three hundred species of invertebrates have been recorded on its main channel.
Like most other chalk streams this is fish stalking country with angler first having to locate trout rising to floating terrestrials or feeding on subsurface nymphs, and without scaring them, cast their imitations upstream to them. Success can depend on stealth and concealment, accuracy of the cast and a fair amount of luck.
It is difficult to put a date on when the method of upstream dry fly fishing first came about on the Itchen, perhaps it dates from the 1880s when Frederick Halford first devised, perfected and then wrote about it on the Test. Some years later GEM Skues pioneered the method of fishing a nymph upstream to trout that he could see feeding just below the surface, and although he was vilified by the dry fly purists for many years, fishing the upstream nymph to trout and grayling is now an acceptable practice.
The river below Winchester supports a good stock of coarse fish with roach, dace, perch, pike and bream featuring in catches during the winter months.
There are also runs of migratory fish. Very few fish run as far upriver as Winchester and most fish are caught by rods spinning lures or fishing the shrimp or prawn. fishing with worms is prohibited. Some years ago the Hampshire river keepers were keen to fish the fly for salmon and they developed a method of fishing a gold headed nymph type fly known as the Hampshire Hog. On spotting a fish the fly was cast upstream and fished down in the same manner as Czech nymph fishing. They had good results with the method at that time, and it is possible they still do. The salmon season opens on the 17th January and closes on 2nd October. In recent years runs of migratory fish have sadly depleted and as a conservation measure all salmon caught, must be returned unharmed to the river.