The busy Napier Street route to the city through Fitzroy will be out of action while Melbourne Water moves on with its project to replace the M41 water main.
Contractors are about to dig under Alexandra Parade outside the Fitzroy pool, a job that requires a tunnel boring machine (TBM).
Site compounds are to be established to launch the TBM, which will then be in operation for five months.
These operations are right on the alignment of the bike route, so riders will need to assess the detour options that are on offer.
The detour map suggests a number of possible routes for riders moving north-south.
There will be extensive use of signs to guide riders to alternative routes.
The principal options are to use Canning, Brunswick or Wellington Streets.
For an east-west connection, Moor and Stanley Streets are suggested.
The existing main is more than 100 years old and supplies water to 350,000 people and to businesses in the inner suburbs.
The project has been moving through the Edinburgh Gardens, but now the activities move further south.
The new main is being installed from the Merri Creek to the MCG.
Part of the new main follows the route of then old main, but some sections follow a new route.
The project will continue through the end of next year. Click here for a detailed map.