Causes of goose dying

[Akutan]

Hi, I am relatively new here and a beginner in poultry rearing. I have 8 goose, three of them got sick recently and one died today. all this three were laying eggs which they never sat on them and I don't know why? these geese are unable to stand or eat anything. their dropping are watery and black in colour with yellow patches. please help

 

[Eggcessive]

Sorry for your loss. Where is your location? Have you checked or mold in your feed or an “off odor?” Are there any plants or dead fish/animals near water or a compost bed they could have eaten? Were they paralyzed and was the neck limp? If you are in the US, most state poultry labs can perform a necropsy to look for a cause of death if the body is kept cold, but not frozen. Here is a list of most state vets:
https://www.metzerfarms.com/PoultryLabs.cfm