Up to 90 motorists a day are taking advantage of the Tuapeka Mouth Ferry's extended Clutha River crossings while the Clydevale bridge is upgraded.
The bridge closed on Monday for a beam and deck upgrade expected to cost $418,052.
It is closed from 7am to 6pm, Mondays to Fridays, and 7am to 5pm on Saturdays until September 30.
Bridge crossings are permitted briefly, from noon to 12.30pm every day, and from 8.45am to 9.15am and 2.45pm to 3.30pm during school terms.
About 10km upstream from the Clydevale bridge, the free ferry is the closest alternative route across the river and is running on extended hours from 8am to noon, and 12.30pm to dusk, Mondays to Saturdays, for suitable vehicles.
With school holidays until the end of next week, the ferry has been kept busy taking motorists across the Clutha River. This week about 90 vehicles used the ferry each day.
The ferry, also called the Tuapeka Mouth Punt, is funded by the Clutha District Council and is treated and used much like a bridge.
It is the only one of its kind in New Zealand, and is believed to be the last water-driven public punt in the southern hemisphere.
It ferries people and vehicles across the Clutha River just downstream from where the Tuapeka River meets the Clutha, 37km northwest of Balclutha.
However, the punt's operation is subject to river conditions.
Council district assets manager Jules Witt said the next-closest alternative crossings are the Beaumont and Balclutha bridges, but those routes could cause a ''potentially significant detour'' of 20 to 30 minutes, depending on where people were going.
The Clydevale bridge spans the Clutha River about 22km northwest of Balclutha. It is a key transport route, as some oversized loads cannot be taken over the Balclutha bridge.
The bridge also serves as an alternative route when the Beaumont bridge, on State Highway 8, is closed for repairs.
Weight restrictions (50% of class 1; 23 tonnes maximum) were placed on the Clydevale bridge in November 2009 after an investigation found it was not initially designed and constructed for class 1 (44-tonne) loads.
The upgrade will restore the bridge to full heavy vehicle capacity.
The New Zealand Transport Agency last year approved its 69% share of funding for the strengthening project, estimated to cost a total of $974,000.
The unused funding from the bridge deck and beam upgrade will be carried over to the 2013-14 year and allocated towards the pile repairs contract.
