A fiber optic cable is being installed below the confluence of the Seine and Oise. Please see below the modifications scheduled and a pictorial attachment.
As part of the project to open the dock for the future Port Seine-Métropole Ouest, the fiber-optic network between Achères and Andrésy must first be rerouted.
These works will require the deployment of marine equipment to excavate the riverbed trench and underwater equipment to install the new fiber-optic connection.
These operations will result in temporary changes to navigation conditions—listed below—at the site of the future structure, starting October 7, 2026:
Modification of signage on the bridges upstream and downstream of the work site. Prohibition of maneuvering or stopping for vessels passing through the work zone. Requirement to contact VHF Channel 10 when approaching the work site. Vessel monitoring at the Conflans-Sainte-Honorine railway bridge.
Please find the intervention dates below and the modified signage plan attached:
From October 7 to October 18, 2026, 07:00 to 18:00: Call for vigilance (fiber-optic detection and site preparation outside the channel on the right bank—Andrésy side—and dredging/trenching works on the right bank in the municipality of Andrésy, outside the navigation channel).
October 19, 2026, 07:00 to 18:00: Change in navigation direction at the Conflans-Sainte-Honorine railway bridge (PK 71.082): Passage No. 2 converted to two-way traffic. Closure of Channel No. 3
October 20 and 21, 2026, from 7:00 AM to 6:00 PM: Channel No. 3 operating with two-way traffic Closure of Channel No. 2
October 22 to 23, 2026: Navigation suspended from 9:00 PM to 6:00 AM, including the Andrésy arm.
October 23, 2026: Closure of the Andrésy arm from 6:00 AM to 6:00 PM.
Becky Gray