For Blessington:
Permits can be obtained from Charles Camping (Tel: 045 – 865351). Gyves shop (Tel: 045 – 865153) in Blessington and from the following outlets in Dublin:- Rory’s, Southside Angling, Henry’s Tallaght Gun & Rod Shop and Angling & Shooting Centre. Boat permits are available from the E.S.B. Fisheries Conservation, Hydro Group, Ardnacrusha, Limerick (Tel: 061 – 345588).
For other places to fish in Dublin see here:
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(Which reminds me I've only been out once so far this year. Time to remedy that).
Murt