The 30ft whale was discovered at Belhaven beach, near Dunbar, late on Sunday night.
Marine experts believe the whale may have been entangled in creel ropes. However the animal is believed to have died for several weeks meaning the animal is too decomposed for this to be confirmed.
Corinne Gordon, of the British Divers Marine Life Rescue, said: “It is believed this whale was entangled. If this was the case then it would not have been able to come to the surface for air so it would have drowned.
“If it was unable to move then it would not have been able to feed either.
“It is a really sad situation but there is absolutely nothing we can do unfortunately.
“I’d urge everyone to keep away from it because whales are full of bacteria so people do not want to go near it.”
Teams from the Scottish Marine Animal Stranding Scheme and East Lothian Council have also been at the scene.
Sam Christopherson, director of Coast to Coast Surf School, said: “We became aware of the whale this morning when one of our teachers went out to give a session.
“It is so big. The whale is definitely a lot bigger than the usual animals that get washed up on this beach. We will usually get a few whales, seals and dolphins a year here.
“It is horrendous for the animal. It’s such a shame to see these kind of incidents.”
A spokesperson for East Lothian Council said: “We are aware of the whale carcass at Belhaven and arrangements have been made by our Countryside Officers, via a specialist contractor, to dispose of it as soon as possible.”
Join our Facebook group Our Edinburgh to share images and news from and around the Capital