The Waitaki District Council began ground testing on the banks and riverbed last week, which involved drilling three test holes and two in the river, a spokesman said.
The tests were conducted from a barge with increased environmental controls in place.
The council secured design funding for a replacement bridge earlier in the year.
"The eventual project will be shovel-ready once construction funding is acquired," the spokesman said.
The bridge is the second to be constructed in that location, with the original piles from its 1871 predecessor still visible at low tide upstream of the existing bridge.
Constructed in 1899, it was originally dubbed the Victoria Bridge, after Queen Victoria, however the name has not stuck.
At the time, the price of the bridge was subject to much debate among the council, which halted the construction.
The original structure was built of New Zealand timber from the Catlins River, which was only expected to last 20 years.
It instead lasted 28 years.
The new bridge, which is still in use today, was constructed from Australian hardwood, which at the time was estimated to last for a century.
Like its predecessor, the bridge has lasted well past expectations.