Access to rivers on private lands is a matter for the landowner. While there is no general right of access, where the fishing rights appurtenant to the land are held by a third party (usually the State, an individual or an angling club), there is a right for such holder (or their assignees) to have reasonable access across private land to the fishery in order to exercise the right to fish.
I am advised by Inland Fisheries Ireland (IFI) that in the case of a river, this usually means defined access and egress across private land at either end of a fishery usually by prior agreement with the landowner and unrestricted access along the river bank for which the fishing right exists for those persons entitled to exercise the right.
My Department, via IFI, manage schemes which are focused on habitat enhancement but not funding schemes to enhance fishing access for fishermen on private lands. I am advised that there may be schemes under the remit of the National Parks and Wildlife Service which could be explored further.