The invaluable KildareStreet.com tells us of this written Dáil question and answer on 4 February 2015:
Martin Heydon [FG, Kildare South]: To ask the Minister for Arts, Heritage and the Gaeltacht if her attention has been drawn to concerns regarding the lack of dredging on the lateral canals of the River Barrow and overgrown vegetation which is making navigation difficult; her plans to improve this situation; and if she will make a statement on the matter.
Heather Humphreys [FG, Clones Sheugh]: I am advised by Waterways Ireland that, as the Barrow Navigation is wholly situated within the River Barrow and River Nore Special Area of Conservation (SAC), due regard must be given to the provisions of the EC (Birds and Natural Habitats) Regulations 2011. These require a rigorous assessment to be carried out to assess the impacts of any work on the protected species and habitats, prior to any works being undertaken.
If the impacts cannot be screened out and a Stage II assessment is required, a full planning application must be made. In addition, the Fisheries Consolidation Act 1959 (as amended) prohibits any in-stream works, such as dredging, during the spawning season from October to June.
I am informed by Waterways Ireland that dredging on the lateral canals of the Barrow Navigation was historically done during the winter months but that this is not now possible. However, Waterways Ireland is working with Inland Fisheries Ireland to formulate procedures which would allow work to be carried out in accordance with the relevant legislation. In addition, Waterways Ireland is continuing to work with all relevant agencies to ensure that as much work as possible is carried out on the Barrow within the time constraints which exist.
I have been assured by Waterways Ireland that it remains fully committed to the development of the Barrow Navigation in line with its statutory remit.
This question produced useful information, whereas some TDs seem to ask questions only as a way of assuring their constituents of their undying love and devotion. See, for instance, Brendan Smith, who has asked the same question at least three times.
Note that the short dredging season presumably applies to other rivers that are within SACs, such as the River Shannon at Plassey.