The project consists of six rock pools that provide a route for fish to gradually move up or down beyond the 2.5m weir.
The structure constitutes the final piece of the ‘fish pass jigsaw’ on the River Derwent, enabling fish to move freely from the River Tyne to the reservoir.
It follows on from similar work at Derwenthaugh and Lintzford which have already proved a success with a greater diversity and density of fish species now found upstream of those sites.
Jack Bloomer, project manager at Tyne Rivers Trust, said: “We want the river to thrive and the realisation of this project will help the Derwent to do this.
“Every year, fish move through our river systems to colonise new areas, exploit different resources and spawn but obstructions like the two and a half metre high weir at Shotley Grove make it impossible for this to happen.
“The construction of fish passes downstream at Derwenthaugh and Lintzford, meant that Shotley Grove Weir was the last remaining major obstruction to fish on the River Derwent until the reservoir.
“This work ensures that all fish populations within the River Derwent will be connected to one another, increasing the gene pool.”
The project was led by the trust and included Durham County Council, the Environment Agency and the Marine Management Organisation through the European Maritime and Fisheries Fund.
Councillor Ossie Johnson, the council’s cabinet member for tourism, culture, leisure and rural issues, said: “This is a fantastic example of how organisations can work together to secure funding and delivery of projects.
“This was the last remaining barrier on the River Derwent and construction of the pass will allow salmon and sea trout to migrate up river to lay their eggs.
“It is a significant investment in the riverine habitat and will enhance ecology and improve angling for clubs.”