ATTEMPTS to salvage a barge that sank and leaked sewage into the River Itchen will begin today.

The MV Humber Star remains partially submerged off Woolston jetty, pictured, four days after she began taking on water and leaking gallons of effluent and red diesel.

The 40-year-old vessel is used by Southern Water to transport treated sewage from Woolston to Marchwood.

The owner of the barge, Oran Environmental Services, said it expected the salvage operation to take about three days.

General manager Alister Veitch said it remained a mystery why the 148ft barge suddenly went down at about 4am on Friday. “Divers have inspected the barge and found no signs of damage to the hull. We probably won’t know until it is put in a dry dock,” he said.

Residents raised the alarm after smelling a foul stench. It is not known how much sludge leaked into the river, a site of special scientific interest, but Mr Veitch said it had stopped leaking.

An insurance assessor has visited the site and appointed a salvage team.

A Southern Water spokesman said it was closely monitoring the situation and waiting for the go-ahead to transfer the sludge still contained in the Humber Star into a replacement barge to be taken to a recycling centre.