OTTAWA -- Parks Canada's crumbling forts, historical houses and other heritage structures are in much poorer shape than the agency estimates.

That's the finding of an independent consultant asked to review a comprehensive inventory created by Parks Canada to determine how much repair work is needed for its varied infrastructure across the country.

The agency's 2012 inventory found that 47 per cent of all its assets -- from dams, bridges and roads, to old stone forts -- are in poor or very poor condition.

But Opus International Consultants Ltd. said its own sampling of hundreds of assets pushed that overall level to 53 per cent.

And so-called cultural assets -- the historical houses, fortifications, locks and other heritage gems from Canada's past -- are in even worse shape.

Opus estimates 61 per cent of these 2,000 structures are in poor or very poor shape, compared with Parks Canada's more rosy assessment of just 33 per cent.

"Results indicate that at the portfolio level the value of (Parks Canada) assets in poor condition has increased from condition reported in the 2012 National Asset Review," says the Opus report, which cost taxpayers $316,000.

A copy of the Dec. 16, 2013, document was obtained by The Canadian Press under the Access to Information Act.

Parks Canada has come under fire in recent years for weak management of its real-estate portfolio, which includes historic canals and archeological sites, in addition to campgrounds, access roads and visitor centres.

An internal evaluation in 2009 slammed officials for failing to maintain a reliable inventory of hundreds of buildings and other structures, estimated to be worth some $15 billion today.

In response, Parks Canada undertook a thorough review of all its assets in 2012 to set a baseline, estimating there was $2.9 billion worth of deferred repairs.

More than half the deferred work was earmarked for waterways, highways and bridges -- so-called high-risk assets -- but Opus found these structures were in better condition than Parks Canada estimated.

Instead, irreplaceable cultural assets were found to be the most neglected, with almost two-thirds requiring about $230 million worth of repairs and maintenance work.

A spokeswoman for Parks Canada said the agency is still reviewing the Opus report, which she said largely backs the inventory estimates about the cost of repair work.

"Parks Canada has invested an average of $119 million annually over the last 10 years on the recapitalization of its infrastructure," Genevieve Patenaude said in an email.

"Investments include incremental capital resources announced by the government, the most recent of which was $19 million announced in Budget 2013 to address critical improvements to national park highways and bridges."

Parks Canada, which operates more than 200 national parks, historic sites and marine conservation areas, has been hit hard since 2012 with budget cuts. The agency lost some 587 staff in 2012-2013, for example, or about 13 per cent of its workforce.

At the same time, 20.6 million people visited its sites in 2012-2013, a three per cent increase and the first rise in visitor numbers in four years.