Families hoping to spend their Easter weekend at a popular Sydney beach will need to make alternate arrangements after it became inundated with mounds of seaweed.

Piles of smelly weed up to two metres deep on some parts of Collaroy Beach, on the Northern Beaches, was shut down by the local council Wednesday.

In a Facebook announcement, Northern Beaches Council said the mountains of weed would likely keep the beach closed for the duration of the long weekend.

Piles of smelly weed up to two metres deep on some parts of Collaroy Beach (pictured), on the Northern Beaches, was shut down by the local council Wednesday

'Collaroy Beach is closed and may be closed this long weekend due to large amounts of seaweed (1-2 metres in some parts!),' its post read.

Removing the unsightly accumulation of sea matter was out of the question, with the Department of Fisheries banning it from being excavated.

'This is a completely natural occurrence and we understand it can be smelly and unsightly but seaweed is a food source, home and shelter to many amazing sea creatures,' the post continued.

Northern Beaches Mayor Michael Regan said so much seaweed had washed up due to 'large swells over the last couple of weeks', Yahoo7 reported.

Northern Beaches Mayor Michael Regan said so much seaweed had washed up due to 'large swells over the last couple of weeks'

'Normally with the large swells we lose sand,' Mr Regan said.

'The seaweed is nature's way of rebuilding the beach as it acts as foundations for the sand to be collected and in turn re-establishes the beach front. It also is great food for beach critters and the local ecosystem.'

Collaroy Beach was the only one to have been affected by the natural incident, with a Surf Life Saving spokesman saying changes were being closely monitored.

'This appears to be a localised issue with no other surrounding beaches impacted by the seaweed, and it is too early to tell if the beach will be closed tomorrow,' he said.