An anchor fly is generally a larger, heavily weighted pattern that is used to get deep quickly and remain in contact with the bottom. They are used in Czech Nymphing and other similar tight line techniques. Originated because many competitions do not allow weight to be added to the line, these flies were created to also act as a sinker. High sink rates are archived by utilizing tungsten beads, lead wire and in some cases slim profiles ( ex. Lance Egan’s Iron Lotus).
Anchor flies are the heaviest in multi-fly rigs, but that does not mean that they all have to be large, use tungsten beads and be loaded with lead wire to do the job. They simply have to be heavy enough to get to the bottom and remain there. While a large heavy fly such as a size 6 GDs Czech Catnip (George Daniel) might be required in faster moving waters such as can be found out west or in the early season creeks of Pennsylvania, in the Driftless Area of Wisconsin a size 14 Bead Head Prince Nymph may be enough to do the job.
There are some excellent books available as well as free on line videos that detail the various nymphing techniques.
Here is a link to part 1 of a three part series by George Daniel on nymphing techniques which includes contact nymphing.
Anchor flies can be purchased in our online store.