The canal towpath on the Lune Aqueduct has been closed due to a sinkhole, says a charity caring for Britain's waterways.
The Canal & River Trust said engineers were working on repairs while also investigating the cause.
The towpath, which is popular with people walking along the canal over the iconic Grade 1 aqueduct at Lancaster, has been fenced off.
A statement on the Canal and River Trust website said: "The towpath at Lune Aqueduct on the Lancaster Canal remains closed due to a sinkhole that has developed along the towpath.
"Our engineers are continuing to work on a method of repair while also investigating the underlying cause. Due to the presence of electricity cables in the area, a full design solution is required before repair works can proceed.
"A further update will be provided on or before Wednesday, 10 June."
The section of towpath has been fenced off. Photo: Canal and River Trust

Residents posting online said there were "large deep holes" on the towpath of at least a foot deep.
The 202 metres (664 feet) long aqueduct carries the canal 16 metres (53 feet) above the River Lune.
It was designed by John Rennie and constructed by Alexander Stevens in 1797. It consists of five 21 metre (70 foot) semi-circular arches.
The Canal and River Trust is the UK's largest canal charity, caring for a 2,000-mile network of waterways.


Man accused of stealing joints of meat at Lancaster Asda by hiding them in his trousers
LISTEN and PHOTOS: Spectacular display of 12,000 poppies unveiled at Lancaster landmark
Eden Project Morecambe boss gives update on early stages of work on new £100m attraction
Lancaster, Morecambe and Carnforth Remembrance services announced
Road closures for pre-Tour de France work announced for Lancaster district
Lancaster rock guitarist braves beard shave for charity
Two arrests made after post office robbery in Lancaster
BBC Philharmonic Orchestra to perform concert for schools at Morecambe Winter Gardens
PHOTOS: Plans go in for major Lancaster regeneration scheme
Lancaster music venue's heartfelt message ahead of final night on New Year's Eve
Morecambe school named among one of England's most improved for attendance
Lancaster hospital nursing boss appointed to University of Cumbria honorary role
Morecambe Football Club placed under another embargo by the National League
£1.5m Lancaster scheme to boost water quality in River Lune is complete
Family pays tribute to Lancaster pensioner who died in road crash
Popular artist's print of Morecambe Bay Academy to be launched at alumni evening
Work set to begin on new Heysham skate park
Light Up Lancaster promises to illuminate city with ‘No Boundaries’
Sadness as Morecambe sports and social club suffers break-in on night of reopening
Man arrested after death of pensioner in Lancaster road crash

