Scariest Pond on the Planet Award goes to.... ME. (a Newbie, too)

[Timothy]

Just to put an oar in the water - so to speak, I respect every one that has answered your question, but if it were me, I think I'd call the county extension and ask them the same question. There's no telling what's at the bottom of this, and a 20'X20' area that's relatively deep could harbor )) any number of things you may not want to deal with. If there is anything detrimental in there you sure wouldn't want to distribute it across the surface of your lawn or even a drainage ditch.
Have you ever seen it clear and functional? How long has it been unattended? Was the rooster fresh? I'm not trying to be amusing, but if his demise was recent it would be different than if he had been in there a long time decaying and contaminating the water with who knows what else. Not to be over dramatic, but you don't know if he drowned, or was poisoned.
I think I'd find out from experts what I was dealing with before I proceeded.

 

[Tula]

Perhaps you could contact the company that did the original work, since you have the invoice, to see if they could advise you?

Truthfully, it sounds like a big undertaking. You said you've lived there for 8 years, are you interested in renovating and maintaining it?

 

[Big Lou]

Does your neighborhood have storm drains? You mentioned a drainage ditch. Do you know where the ditch terminates?

Do not let our questions scare you. We all truly hope to provide helpful advice.

 

[Becky]

Welcome to the forum