This is what Dave references and is the only leader limit I am aware of (applies to FFO).
§ 65.14. Catch and release fly-fishing only.
(a) The Executive Director, with the approval of the Commission, may designate waters as catch and release fly-fishing only. The designation of waters as catch and release fly-fishing only shall be effective when the waters are so posted after publication of a notice of designation in the Pennsylvania Bulletin.
(b) It is unlawful to fish in waters designated and posted as catch and release fly-fishing only except in compliance with the following requirements:
(1) Fishing may be done with artificial flies and streamers constructed of natural or synthetic materials so long as all flies are constructed in a normal fashion with components wound on or about the hook or hooks. Use or possession of any other lures or substances is prohibited.
(2) Fishing shall be done with tackle which is limited to fly rods, fly reels and fly line with a maximum of 18 feet in leader material or monofilament line attached. Spinning, spincast and casting rods and reels are prohibited.
(3) No trout may be killed or had in possession.
(4) Open to fishing year-round.
(5) Taking of baitfish or fishbait is prohibited.
(6) Wading is permitted unless otherwise posted.
(7) A current trout/salmon permit is required.
(c) Notwithstanding the requirements of this section an angler in a boat may possess bait and fish caught in compliance with the seasons, sizes and creel limits in effect for the water from which taken, provided that the boat angler floats through the catch and release fly-fishing only area without stopping or engaging in the act of fishing or the boat angler puts in or takes out his boat at an access point within the catch and release fly-fishing only area.