Is it proper to say was debris or were debris?

was debris

"Debris" is an uncountable noun. Following is an explanation from the dictionary with examples:

debris

debris

Debris is pieces from something that has been destroyed or pieces of rubbish or unwanted material that are spread around.

I stood at the foot of the collapsed tower and watched the rescue workers sifting through the debris.

A number of people were killed by flying debris.

N-UNCOUNT

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