diarrhia pekin ducks

[starryeyes]

hi we have 4 pekin baby ducks about 4 weeks old . I came home and put them in a new larger home when i went to get there water i saw they had pooped blk diarrhia and it smelt so bad :O sorry for the TMI LOl so what can be wrong with them we keep there area clean they get fresh water several times a day. any help would be great