“De” rhymes with “they”. A little more emphatic with each repeat. Use gestures.

De moose, de mooose (de moose, de mooose)
Swimming in da wata (swimming in da water)
Eating his suppa (eating his suppa)
Where di' 'e go? (where di' 'e go?)
He go… to… sleep (He go… to… sleep)

Repeat several times; end with:

Dead moose, dead moose
Floating in da wata
Not eating his suppa
Where di' 'e go?
He de… com… pose…