Temporary three-way traffic lights are causing delays this afternoon.
There are queues at the junction of Allum Lane and Deacons Hill Road in Borehamwood.
It is causing tailbacks along Shenley Road and back to the waste recycling centre in Allum Lane in the other direction.
Affinity Water is carrying out "essential maintenance". Work is scheduled to continue until tomorrow (Wednesday).
There are also traffic lights on Theobald Street at Borehamwood Shopping Park.
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