Work includes rebuilding canal-side walls and clearing vegetation off locks.
Built by the Swansea Canal Navigation Company between 1794 and 1798, the canal runs 16.5 miles (26.5km) from Swansea to Hen Neuadd in Powys.
But since 1958, parts have been abandoned, sold off and filled in.
"It could take many, many years - decades - before we can see the first boats go down the full length of canal because there's so much work to be done," said Joe Coggins, from Glandwr Cymru, the canal and river trust in Wales.
"These are small building blocks and the work being carried out this week is part of the wider project."
The canal was built primarily to carry coal down to Swansea Docks with the main cargos of coal, iron and steel making the enterprise profitable.
The canal was sold to the Great Western Railway in 1873 and it continued to make a profit until 1895.
A period of decline followed with commercial traffic ceasing in 1931 but horse-towed maintenance boats continued until 1958.
Parts of the canal were then abandoned, sold off and filled in.
Glandwr Cymru inherited a central section of the canal, approximately five miles between Clydach and Ynysmeudwy.
The five locks in it are not navigable with gates removed but weirs are used to ensure water supply to Mond Nickel works at Clydach.
The canal is now popular among towpath users and the Swansea Canal Society is doing the restoration.
Swansea Canal Society and the Waterway Recovery Group are doing the work along the canal, supported by Glandwr Cymru.
"We are responsible for our section, caring for it and keeping it open," Mr Coggins added.
"This work is a great example of where we've gained support with these volunteer groups."

Hilda Gaddum, the mayor of Cheshire East, said her fellow Conservative Michael Jones's position had become "untenable".
The council waived its own financial rules three times when granting Core Fit Ltd contracts totalling £156,000.
Mr Jones said he was "clear" that he had "not misled council".
The fitness company runs classes in schools and is owned by Mr Jones's personal physiotherapist, Amanda Morris. Neither Ms Morris nor her company have commented on the claims.
Mr Jones has previously said he had publicly declared his interest in the firm, while a council spokesman said there had been no "unlawful expenditure or any breach of EU procurement rules".
However, Ms Gaddum said Mr Jones had "misled" councillors at a meeting in October, where he questioned why his link with the company was "being brought up", and had lobbied for it to receive help.
The BBC has seen a letter written by Mr Jones to local MP George Osborne - whose Tatton constituency is included within Cheshire East - in which work carried out by Ms Morris's company is praised.
Emails released following a BBC Freedom of Information Act request show Mr Jones helped Ms Morris write a positive assessment of how Core Fit had fulfilled one of the council's contracts.
Core Fit Ltd contracts
June 2014
March 2015
Ms Gaddum said she had written to Mr Jones asking for his resignation, which led to "a very, very difficult meeting with him".
In a statement, Mr Jones said he would "not be resigning but thank the mayor for recognising the many good things I have achieved".
"I am disappointed, given that I vigorously sponsored her mayoralty to my group, at the comments made. But that is Hilda for you."
The council has not responded to requests for a comment.
Volunteers are helping to restore the historic Swansea Canal as part of a project to bring the full length of the waterway back into use for boats.
[NEXT_CONCEPT]
The leader of Cheshire East Council has rejected a call to resign over claims he "misled" councillors about contracts awarded to his physiotherapist's firm.