The tide was expected to start dropping from 2330 BST
An attempt to coax a 33ft (10.1m) whale into The Solent after it became stranded in shallow water has been called off for the night.
The The Northern Bottlenose whale was spotted off the Hampshire coast on Thursday morning sparking fears it could beach on a sandbank.
The six-tonne mammal is said to be 3,000 miles (4,828 km) off course.
The British Divers Marine Life Rescue has asked people to avoid the area as further activity could cause distress.
Rescuers also said extra boats in the water could block the whale from moving away.
The tide is expected to rise until 2330 BST before it starts dropping which is when the animal could be in danger of beaching.
Stephen Marsh, a marine mammal medic, said: "We got people out there at 1005 BST and it has been monitored all day.
"It looks like the same species that was up the River Thames a few years ago.
"The problem is this species is a deep diving whale and the closest water of depth required is off the Bay of Biscay, about a two-day cruise for a whale.
"The trouble is they feed on deep-sea squid and there aren't many of them in the English Channel.
"Another problem is they don't drink water, they get all their fluids from food they eat so it may not be getting fluids.
"We are hoping if it does strand we will get it onto a pontoon, get a couple of boats either side and tow it out south of the Isle of Wight and point it in right direction and let it go."
The rescue attempt was abandoned at about 2100 BST and was due to be restarted on Friday morning.
Solent Coastguard said it was not warning ships to avoid the area but was monitoring the situation.