The White Bridge in Hartsholme Country Park will be closed until further notice while work on the bridge takes place.
The bridge by the lake of the park closed on July 3 after it was deemed unfit for public use.
During a routine inspection of the bridge, it was found the steelwork on the bridge is deteriorating.
Repairs will be carried out while the bridge is closed.
Residents using the park are being advised of the alternative routes around the park to get from one side on the lake and river to the other, which can be found on boards around the reserve.
Caroline Pritchard, Community Services Manager at the City of Lincoln Council, said: “We know that the White Bridge is used regularly by visitors to Hartsholme Country Park, but we must think of public safety, and have taken advice from our contractors that it must be closed until it is made safe.
“We have displayed alternative routes within the country park, and hope visitors will still go to Hartsholme and take this opportunity to take in different views of the lake.”