A 130-year-old weir on the river Thames in need of repairs is to be updated as works are set to begin this month.

Molesey Weir B, part of the wider Molesey weir and lock complex, was built in 1883 and had its last period of major repairs in 1934.

The weir is set for a significant upgrade after surveys revealed the steel structure was in poor condition and needed to be replaced.

The weir’s 15 buck gates, steel supports and walkways will be removed and replaced with seven radial gates and new surrounding structures.

The existing fish trap will be replaced with a fish pass which will allow a wider variety of fish to pass through the weir without human intervention. The recently installed eel pass will also be retained.

A shingle roof will be retained to ensure the weir blends into the surrounding environment.

David Blythin, project manager at the Environment Agency, said: “After a period of consultation with local residents and river users aimed at minimising disruption, we are now in a position to start work on this major project to upgrade Molesey Weir.

“Work will be carried out in two stages and across two summer seasons during this year and in 2014.

“We do not work during the winter months because higher rainfall will generally increase the flow of water in the river, meaning all weirs have to be fully functional to help manage river levels.”

Work will start this month and will be completed in autumn 2014.

A temporary bridge will be installed while work is carried out to allow residents and boat owners’ access to nearby Ash Island.