mold in little bubbler?

i left my bubbler at a friends house because i couldnt take it with me where i was going and i just got it back about a week an a bit later and i filled it up had a couple bowls and looked in the bottom and there was fairly large chunks of white stuff floating around in the water...

and they "said" they never used it... just wondering if it could be mold? or something else
 
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