A exclusion zone will be been set up on part of the beach in St Aubin's Bay as drainage work gets underway.
A new surface water pipe and outfall is being created to separate surface water from the sewer system.
The project, by the government's Infrastructure and Environment department, is expected to go on until mid-October.
It includes providing for a new surface water connection to a new hospital at Overdale.
During the works, some some parking in Layby 2 on Victoria Avenue will be suspended, and part of the beach blocked off. Signs and water buoys will be in place, and the public is being asked to observe them.
Cyclists using the promenade might be asked to dismount during some of the work.
Work to clad the outfall with granite will continue after October.

Storm Austen: Clean-up continues
Storm Austen: All you need to know
Haut Du Mont: Jury fails to reach verdict on third gas worker
Storm Austen: Government schools to close on Friday
Haut du Mont: Gas workers convicted of manslaughter
Campaign encourages potential child sex offenders to seek help
Electric car charger grant to end in December
Consultation launched on hate crime legislation