What can it be?

[9rounds]

Any idea what this might be? Not in a tank. Sorry about this. But I need answers on what this is. And y'all are the experts.

 

[Chrisv.]

Can we have a little more context?

 

[9rounds]

Can we have a little more context?

Yes. What would you like to know? The jar sat outside for 2.5 yes. Never collected any water. After a heavy week of rain. The jar took in water. Shortly after. I noticed this growth. Unfortunately I lost from start to current pics when my phone broke. So I only have current pics.