Napier's Inner Harbour will undergo dredging for between 20 and 30 days, beginning on Monday, March 25.
A Napier City Council spokeswoman said the dredging may result in water in the Inner Harbour or the estuary appearing brown.
This was because of sediment being churned up during the dredging process.
"A programme of testing is ensuring that disturbed sediments are safe, but in the interests of safety we recommend that people stay out of the water until the water returns to normal," the spokeswoman says.
"The time it will take for the sediment to settle will depend on tidal flows and the size of the sediment particles. Steps will be taken to minimise the spread of sediment within the Inner Harbour and estuary."
Dredging was an essential measure to ensure all vessels entering and exiting the harbour can do so safely, she said.
Vessels will be able to use the harbour while dredging is under way. Fishing and recreational use of the harbour and estuary will not be restricted. Some minor delays may be experienced while the narrowest parts of the channel are dredged.
Hawke's Bay Regional Council has provided consent for the work to be undertaken. A large barge and digger will be visible in the inner harbour during dredging. It is anticipated that the dredging will take 20 to 30 days.