The orange security fence designed to protect the docked navy ships hasn't proved durable. (CBC)

A floating barrier designed to foil terrorist attacks and protect Canadian navy ships cannot handle the rigours of Halifax harbour.

The 1.6-kilometre fence has been dismantled because it was weighed down by mussels and kelp and battered by waves.

"It's definitely a tricky spot," said Dennis Smith, CEO of Whispr Wave, a New Jersey company that has built similar floating fences for navies around the world.

The orange fence acted as a first line of defence for the destroyers and frigates docked near downtown Halifax, thwarting potential attacks from small boats carrying explosives. Its hard plastic teeth jutted 1.5 metres into the air.

In 2006, when the floating fence was announced, the navy said it would cost about $3.5 million. Installation of the boom began a year later.

Smith said the barrier along the Halifax waterfront was under-engineered from the start.

"It's just constant 24/7-365 pounding of the product," he told CBC News.

The navy declined an interview about the floating fence. In a statement, a spokesman said the boom has been removed for scheduled maintenance and would be reinstalled at some point.

"The boom is one of the force protection tools in our toolbox. [Its] employment is adjusted as required based on our needs at any particular time. Now is a good time to conduct planned maintenance such as this," said spokesman Mike Bonin.

But a source told CBC News that only small sections of the fence would be deployed to protect visiting U.S. navy ships, as security for Canadian navy ships isn't considered as pressing.