The mammal, found on the Isle of Harris, was cut open to release net, rope and plastic cups.
The mammal was cut open to release around 100kg of net, bundles of rope, plastic cups, bags, gloves, packing straps and tubing after it was discovered stranded on Luskentyre beach on Thursday.
Experts described the amount of plastic as “horrific” and said it shows the “hazards” litter pose to marine life.
A statement from Scottish Marine Animals Stranding Scheme said: “By the time we got to it, it had been dead for 48 hours and pretty much most of the guts blew out of the side when we stuck a knife in it.
“Animals this size are so well insulated that even though the temperature outside barely got above freezing, they don’t cool down and hence decompose incredibly quickly.
“In this whale’s stomach was approximately 100kg of marine debris a whole range of plastic including sections of net, bundles of rope, plastic cups, bags, gloves, packing straps and tubing.
“All this material was in a huge ball in the stomach and some of it it looked like it had been there for some time.
“The animal wasn’t in particularly poor condition, and whilst it is certainly plausible that this amount of debris was a factor in its live stranding, we actually couldn’t find evidence that this had impacted or obstructed the intestines.
“This amount of plastic in the stomach is nonetheless horrific, must have compromised digestion, and serves to demonstrate, yet again, the hazards that marine litter and lost or discarded fishing gear can cause to marine life.”