McNabs Island in Halifax harbour played a key role during both world wars. (CBC)

Volunteers who clean the beaches on McNabs Island say the federal government is not keeping a promise to clean and maintain the national historic site.

Cathy McCarthy, the president of the Friends of McNabs Island Society, said when volunteers travelled to the island on Oct. 14, it was clear no work had been done near Fort McNab.

"We were disappointed Parks Canada has not been able to mow the grass in the graveyard," she said.

"There's a lot of bushes and trees growing up and even Japanese knotweed has invaded the graveyard."

Earlier this year, Parks Canada cancelled its $1,500 annual volunteer agreement with the Friends of McNabs Island Society, which has cleaned up Fort McNab on McNabs Island for the past 17 years.

The volunteer group has used the money to clean up garbage, look after the cemetery and provide general cleanup work to the fort, which played a key role in protecting the city during both world wars.

McCarthy said the society has offered to find ways to continue the cleanup effort and pay for their costs. She said several New Democrat MPs in Nova Scotia have written to Peter Kent, the federal Minister of the Environment, asking him to reconsider the cancellation of the agreement.

Mike Tilley, who runs a tour boat to McNabs Island, said others could do the work if the federal government was unwilling.

"One of the big things, especially if you enjoy history, is the McNab family cemetery and right now the grass is almost up over the headstones so that's not good," he said.

"If they're not willing or able to do a little bit of maintenance at the graveyard and fort, why can't they let the Friends of McNabs Society or the Gateway House Community of Eastern Passage get involved?"

A spokesperson for Parks Canada told CBC News it will do maintenance work on the fort and the graveyard in the coming weeks.

McCarthy said the Friends of McNabs Island Society will still be doing cleanups of the beach, although they are no longer permitted to clean the area near the fort.

Since 1991, their volunteers have collected more than 10,670 bags of garbage and recyclables from the shorelines of McNabs, Lawlor Islands Provincial Park and the Fort McNab National Historic Site.