Fire crews along with Hillhead Coastguard Rescue Team and Portsmouth Coastguard Rescue Team and police were called to the incident in Portsmouth Harbour just before 5am.
The woman was able to escape the thick sludge and make her way back to shore.
A spokesman for HM Coastguard said: ‘We were called along with other emergency services to a woman stuck in the mud in the harbour. The woman had self recovered by the time we arrived but was assisted by the fire service.’
Hillhead coastguards posted on Twitter they were ‘tasked to a person stuck in the mud’ before adding: ‘Casualty rescued to safety and team re-tasked to another incident.’