Signs, albeit small ones, have been placed at entranceways to the sea advising against swimming for a short time, with the dumping beginning on 16 May.
The all-clear will be given once acceptable water quality results are returned which usually takes five days.
Sewage was also drained into the sea in early April as part of the same project, with “excellent” water results returned and swimming advisories withdrawn.
“We remain committed to transparency, so will release the results no matter what they say,” Guernsey Water said.
“We have liaised closely with the Office of Environmental Health and Pollution Regulation, outlining why this needs to happen and they have accepted our proposals for minimising risk to the environment and public health.”
Pictured: Paper notices have been taped to existing metal signs advising against swimming.
It said the project would prevent future sewage outfalls during future maintenance inspections.
Water Quality Risk Manager Daffyd Griffiths said: “I want to thank the public for heeding our advice last time, we know this can be a popular area but it is essential for these upgrades to happen. Without them the station would eventually fail altogether and that would cause a much bigger problem.
“We do not anticipate any long-term impact and will be releasing the sample results as soon as we get them. We thank everyone in advance for their co-operation.”
Work began on the replacement in mid-March and it’s currently scheduled to complete in the first week of June.