Two people were helped back to safety thanks to a Coastguard team's quick efforts.
The Hartlepool Coastguard Rescue Team and colleagues from Seaham were called out just after 4.30pm yesterday to a report of a woman threatening to jump into the town's marina.
Cleveland Police Cleveland Fire Brigade were already on scene when the Coastguard arrived.
A spokesman for the Coastguard team said: "Once we arrived we kitted up in water rescue gear and waited while negotiators talked to the female.
"Hartlepool RNLI sat off from the wall on standby just in case.
"Just as negotiations seemed to be working the female decided to jump and she swam off in the marina.
"One person from RNLI crew and one member of the coastguard entered the water after a short swim around we then proceeded to detain the casualty and place her onto the waiting lifeboat.
"The casualty was then handed over to the custody of the police."
While the incident was happening, Seaham's team received a second 999 call reporting a man with learning disabilities who had got stuck on the cliffs at Blackhall, and left the marina incident in the hands of their Hartlepool colleagues.
A spokesman for the Seaham officers said: "We arrived on scene and liaised with the police to locate the male in question.
"Once we found the casualty we prepared a rope rescue setup.
"By this time Hartlepool Coastguard had arrived from the first call to give support.
"A cliff tech was lowered down to the casualty who was then put into a rescue harness.
"After the tech reassured the casualty everything was going to be OK, they were both lowered to the cliff bottom and the casualty was handed over into the care of the police."
The call out was also attended Hartlepool RNLI.