I did find 2 interesting articles about Negril’s Great Morass. Both quite old though and neither mention why it is closed

Develop Royal Palm Reserve into attraction — EU head
http://www.jamaicaobserver.com/news/...-head_15145048
September 27, 2013

“Head of the EU delegation Paola Amadei has made a pitch for the Government of Jamaica to promote Royal Palm Reserve in Sheffield as a tourist attraction.
The reserve is a 298-acre peat bog named for the country's endemic Royal Palm or "swamp cabbage", which are distributed only in western Jamaica. It features a mile-long boardwalk through a forest that is home to myriad species of flora and fauna, several of which are found only on the island.
"I find it a wonderful environment and a treasure that should be more widely known. So, I think it's a very good opportunity also to make a pitch in order for the Ministry of Tourism or the Ministry of Environment to make Royal Palm Reserve one of the strong points of the promotion of this part of the country," the EU ambassador said.”

Gov't hunts grant funding to solve Negril's problems
http://www.jamaicaobserver.com/magaz...blems_13286262
January 20, 2013

"Only recently, details of the US$3-million Conservation of the Negril Great Morass and the Rehabilitation of the Royal Palm Reserve Project was revealed.
That project has as its objective "the restoration of historical hydrological regimes based on localised habitat and priority use requirements; the enhancement and re-establishment of natural vegetation communities that provide habitat to wetland fauna; the elimination of conflicts that degrade biodiversity and ecosystem functions; and the implementation of institutional arrangements to ensure long-term sustainability of the wetlands."
In short, the Government is looking at resuscitation of the wetlands in the area and the education of communities to bring people up to speed on how their actions impact the environment and, by extension, their bottomline over the long term."