The fire and rescue service says the unknown substance found on Garwick Beach on Boxing Day was most likely palm oil.
Firefighters say though the risk to humans is low, if dogs eat it, it can be serious.
People are still being asked to avoid touching or removing the yellowy material from the beach south of Laxey.
Meanwhile the coastguard is warning people to keep dogs away from the area until the tide has washed leftover pieces away.
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