Part of the river Wansbeck will be returned to its original course after the construction of a flood storm dam as part of the Morpeth flood scheme.
The river was reinstated along its original route in Mitford this week.
For the past 12 months it has been flowing along a temporary 100-metre channel to allow the dam to be built.
Now the dam construction is nearly complete, the watercourse will be diverted to its original route, which will flow through a number of culverts beneath the dam.
When heavy rainfall increases the water level in the Wansbeck, the culverts restrict the amount of water that is able to flow downstream through Morpeth, reducing flood risk to the town.
The culverts within the dam walls feature special channels that allow fish, crayfish and lamprey to travel upstream.
Before the river was diverted last year, the Environment Agency removed native white-clawed crayfish from the original course of the Wansbeck, relocating them to a safe new home upstream of the dam.
It is possible that some crayfish may have moved into the temporary channel during the past year, so it will be checked for the animals before it is closed off and refilled.
Anthony Myatt, project manager at the Environment Agency, said: “The diversion of the Wansbeck was vital to allow the construction of the flood storage dam, and now we are at the important stage of directing it back under the new dam.
“The culverts at the bottom of the dam will then control the rate of flow of the river in times of high rainfall, keeping the river at a safe level in Morpeth.
“This key feature of the town’s flood defence scheme is complemented by improved flood defences in the town itself.”
Once the river has been diverted to its original course we will be able to start the earthworks to build the dam embankment.